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  18. <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端" class="dropdown-title"><a href="/blog/web/" class="link-title">前端</a> <span class="title" style="display:none;">前端</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>前端文章</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/blog/pages/8143cc480faf9a11/" class="nav-link">JavaScript</a></li></ul></li><li class="dropdown-item"><h4>学习笔记</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/blog/note/javascript/" class="nav-link">《JavaScript教程》</a></li><li class="dropdown-subitem"><a href="/blog/note/js/" class="nav-link">《JavaScript高级程序设计》</a></li><li class="dropdown-subitem"><a href="/blog/note/es6/" class="nav-link">《ES6 教程》</a></li><li class="dropdown-subitem"><a href="/blog/note/vue/" class="nav-link">《Vue》</a></li><li class="dropdown-subitem"><a href="/blog/note/react/" class="nav-link">《React》</a></li><li class="dropdown-subitem"><a href="/blog/note/typescript-axios/" class="nav-link">《TypeScript 从零实现 axios》</a></li><li class="dropdown-subitem"><a href="/blog/note/git/" class="nav-link">《Git》</a></li><li class="dropdown-subitem"><a href="/blog/pages/51afd6/" class="nav-link">TypeScript</a></li><li class="dropdown-subitem"><a href="/blog/pages/4643cd/" class="nav-link">JS设计模式总结</a></li></ul></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="页面" class="dropdown-title"><a href="/blog/ui/" class="link-title">页面</a> <span class="title" style="display:none;">页面</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/8309a5b876fc95e3/" class="nav-link">HTML</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/0a83b083bdf257cb/" class="nav-link">CSS</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="技术" class="dropdown-title"><a href="/blog/technology/" class="link-title">技术</a> <span class="title" style="display:none;">技术</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/9a7ee40fc232253e/" class="nav-link">技术文档</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/4c778760be26d8b3/" class="nav-link">GitHub技巧</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/117708e0af7f0bd9/" class="nav-link">Nodejs</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/41f87d890d0a02af/" class="nav-link">博客搭建</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="更多" class="dropdown-title"><a href="/blog/more/" class="link-title">更多</a> <span class="title" style="display:none;">更多</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/f2a556/" class="nav-link">学习</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/aea6571b7a8bae86/" class="nav-link">面试</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/2d615df9a36a98ed/" class="nav-link">心情杂货</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/baaa02/" class="nav-link">实用技巧</a></li><li class="dropdown-item"><!----> <a href="/blog/friends/" class="nav-link">友情链接</a></li></ul></div></div><div class="nav-item"><a href="/blog/about/" class="nav-link">关于</a></div><div class="nav-item"><a href="/blog/pages/beb6c0bd8a66cea6/" class="nav-link">收藏</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="索引" class="dropdown-title"><a href="/blog/archives/" class="link-title">索引</a> <span class="title" style="display:none;">索引</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/categories/" class="nav-link">分类</a></li><li class="dropdown-item"><!----> <a href="/blog/tags/" class="nav-link">标签</a></li><li class="dropdown-item"><!----> <a href="/blog/archives/" class="nav-link">归档</a></li></ul></div></div> <a href="https://github.com/heBody/blog" target="_blank" rel="noopener noreferrer" class="repo-link">
  19. GitHub
  20. <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav></div></header> <div class="sidebar-mask"></div> <div class="sidebar-hover-trigger"></div> <aside class="sidebar" style="display:none;"><div class="blogger"><img src="https://fastly.jsdelivr.net/gh/xugaoyi/image_store/blog/20200103123203.jpg"> <div class="blogger-info"><h3>彪哥</h3> <span>爱好前端</span></div></div> <nav class="nav-links"><div class="nav-item"><a href="/blog/" class="nav-link">首页</a></div><div class="nav-item"><a href="http://fseller.com" target="_blank" rel="noopener noreferrer" class="nav-link external">
  21. 个人游戏网站
  22. <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端" class="dropdown-title"><a href="/blog/web/" class="link-title">前端</a> <span class="title" style="display:none;">前端</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>前端文章</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/blog/pages/8143cc480faf9a11/" class="nav-link">JavaScript</a></li></ul></li><li class="dropdown-item"><h4>学习笔记</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/blog/note/javascript/" class="nav-link">《JavaScript教程》</a></li><li class="dropdown-subitem"><a href="/blog/note/js/" class="nav-link">《JavaScript高级程序设计》</a></li><li class="dropdown-subitem"><a href="/blog/note/es6/" class="nav-link">《ES6 教程》</a></li><li class="dropdown-subitem"><a href="/blog/note/vue/" class="nav-link">《Vue》</a></li><li class="dropdown-subitem"><a href="/blog/note/react/" class="nav-link">《React》</a></li><li class="dropdown-subitem"><a href="/blog/note/typescript-axios/" class="nav-link">《TypeScript 从零实现 axios》</a></li><li class="dropdown-subitem"><a href="/blog/note/git/" class="nav-link">《Git》</a></li><li class="dropdown-subitem"><a href="/blog/pages/51afd6/" class="nav-link">TypeScript</a></li><li class="dropdown-subitem"><a href="/blog/pages/4643cd/" class="nav-link">JS设计模式总结</a></li></ul></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="页面" class="dropdown-title"><a href="/blog/ui/" class="link-title">页面</a> <span class="title" style="display:none;">页面</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/8309a5b876fc95e3/" class="nav-link">HTML</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/0a83b083bdf257cb/" class="nav-link">CSS</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="技术" class="dropdown-title"><a href="/blog/technology/" class="link-title">技术</a> <span class="title" style="display:none;">技术</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/9a7ee40fc232253e/" class="nav-link">技术文档</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/4c778760be26d8b3/" class="nav-link">GitHub技巧</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/117708e0af7f0bd9/" class="nav-link">Nodejs</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/41f87d890d0a02af/" class="nav-link">博客搭建</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="更多" class="dropdown-title"><a href="/blog/more/" class="link-title">更多</a> <span class="title" style="display:none;">更多</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/f2a556/" class="nav-link">学习</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/aea6571b7a8bae86/" class="nav-link">面试</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/2d615df9a36a98ed/" class="nav-link">心情杂货</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/baaa02/" class="nav-link">实用技巧</a></li><li class="dropdown-item"><!----> <a href="/blog/friends/" class="nav-link">友情链接</a></li></ul></div></div><div class="nav-item"><a href="/blog/about/" class="nav-link">关于</a></div><div class="nav-item"><a href="/blog/pages/beb6c0bd8a66cea6/" class="nav-link">收藏</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="索引" class="dropdown-title"><a href="/blog/archives/" class="link-title">索引</a> <span class="title" style="display:none;">索引</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/categories/" class="nav-link">分类</a></li><li class="dropdown-item"><!----> <a href="/blog/tags/" class="nav-link">标签</a></li><li class="dropdown-item"><!----> <a href="/blog/archives/" class="nav-link">归档</a></li></ul></div></div> <a href="https://github.com/heBody/blog" target="_blank" rel="noopener noreferrer" class="repo-link">
  23. GitHub
  24. <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav> <ul class="sidebar-links"><li><a href="/blog/pages/f344d070a1031ef7/" class="sidebar-link">ECMAScript 6 简介</a></li><li><a href="/blog/pages/c1edd70a6b7c7872/" class="sidebar-link">let 和 const 命令</a></li><li><a href="/blog/pages/b1ab10a62f7564da/" class="sidebar-link">变量的解构赋值</a></li><li><a href="/blog/pages/ca89eca8adeba5f4/" class="sidebar-link">字符串的扩展</a></li><li><a href="/blog/pages/a650b4a0ebfc9350/" class="sidebar-link">字符串的新增方法</a></li><li><a href="/blog/pages/0473261a6ab0ee8c/" class="sidebar-link">正则的扩展</a></li><li><a href="/blog/pages/5dfea9a0f2d1a392/" class="sidebar-link">数值的扩展</a></li><li><a href="/blog/pages/8ed309d668b20264/" class="sidebar-link">函数的扩展</a></li><li><a href="/blog/pages/e34009d60d8bc4b2/" class="sidebar-link">数组的扩展</a></li><li><a href="/blog/pages/b5e3e0a0ff6e9c25/" class="sidebar-link">对象的扩展</a></li><li><a href="/blog/pages/e85e68947502cf90/" class="sidebar-link">对象的新增方法</a></li><li><a href="/blog/pages/02c86eb2792f3262/" class="sidebar-link">Symbol</a></li><li><a href="/blog/pages/0c21dae358fca16b/" class="sidebar-link">Set 和 Map 数据结构</a></li><li><a href="/blog/pages/f56ec2ab97d60483/" class="sidebar-link">Proxy</a></li><li><a href="/blog/pages/74de3e45e4491e95/" aria-current="page" class="active sidebar-link">Reflect</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/blog/pages/74de3e45e4491e95/#概述" class="sidebar-link">概述</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/74de3e45e4491e95/#静态方法" class="sidebar-link">静态方法</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-get-target-name-receiver" class="sidebar-link">Reflect.get(target, name, receiver)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-set-target-name-value-receiver" class="sidebar-link">Reflect.set(target, name, value, receiver)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-has-obj-name" class="sidebar-link">Reflect.has(obj, name)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-deleteproperty-obj-name" class="sidebar-link">Reflect.deleteProperty(obj, name)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-construct-target-args" class="sidebar-link">Reflect.construct(target, args)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-getprototypeof-obj" class="sidebar-link">Reflect.getPrototypeOf(obj)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-setprototypeof-obj-newproto" class="sidebar-link">Reflect.setPrototypeOf(obj, newProto)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-apply-func-thisarg-args" class="sidebar-link">Reflect.apply(func, thisArg, args)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-defineproperty-target-propertykey-attributes" class="sidebar-link">Reflect.defineProperty(target, propertyKey, attributes)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-getownpropertydescriptor-target-propertykey" class="sidebar-link">Reflect.getOwnPropertyDescriptor(target, propertyKey)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-isextensible-target" class="sidebar-link">Reflect.isExtensible (target)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-preventextensions-target" class="sidebar-link">Reflect.preventExtensions(target)</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/74de3e45e4491e95/#reflect-ownkeys-target" class="sidebar-link">Reflect.ownKeys (target)</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/blog/pages/74de3e45e4491e95/#实例-使用-proxy-实现观察者模式" class="sidebar-link">实例:使用 Proxy 实现观察者模式</a></li></ul></li><li><a href="/blog/pages/2810ae8985e9bd52/" class="sidebar-link">Promise 对象</a></li><li><a href="/blog/pages/48df907ad3570f3d/" class="sidebar-link">Iterator 和 for-of 循环</a></li><li><a href="/blog/pages/718b48ed9ce0adce/" class="sidebar-link">Generator 函数的语法</a></li><li><a href="/blog/pages/75af7031eb66847b/" class="sidebar-link">Generator 函数的异步应用</a></li><li><a href="/blog/pages/3777253e65bac487/" class="sidebar-link">async 函数</a></li><li><a href="/blog/pages/e831e1593c82bbe0/" class="sidebar-link">Class 的基本语法</a></li><li><a href="/blog/pages/83f8c3a0cd87dd83/" class="sidebar-link">Class 的继承</a></li><li><a href="/blog/pages/efe2fb04eb8ac5fb/" class="sidebar-link">Module 的语法</a></li><li><a href="/blog/pages/a79ca2e64ceae213/" class="sidebar-link">Module 的加载实现</a></li><li><a href="/blog/pages/984bf549204bb266/" class="sidebar-link">编程风格</a></li><li><a href="/blog/pages/32c35f7651d6e58e/" class="sidebar-link">读懂 ECMAScript 规格</a></li><li><a href="/blog/pages/16121351be68691b/" class="sidebar-link">异步遍历器</a></li><li><a href="/blog/pages/a2ba314746bfdbdd/" class="sidebar-link">ArrayBuffer</a></li><li><a href="/blog/pages/7188882b8d65af1b/" class="sidebar-link">最新提案</a></li><li><a href="/blog/pages/e97bc1e5626b082c/" class="sidebar-link">装饰器</a></li><li><a href="/blog/pages/1cf50330655efc69/" class="sidebar-link">函数式编程</a></li><li><a href="/blog/pages/6a8e2dc558da1b39/" class="sidebar-link">Mixin</a></li><li><a href="/blog/pages/8e8f80f69b775a56/" class="sidebar-link">SIMD</a></li><li><a href="/blog/pages/ea6f3b870f6dab69/" class="sidebar-link">参考链接</a></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/blog/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><a href="/blog/note/es6/#《ES6 教程》笔记" data-v-06225672>《ES6 教程》笔记</a></li></ul> <div class="info" data-v-06225672><div title="作者" class="author iconfont icon-touxiang" data-v-06225672><a href="javascript:;" data-v-06225672>阮一峰</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2020-02-09</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="data:image/png;base64,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">Reflect<!----></h1> <div class="theme-vdoing-content content__default"><h1 id="reflect"><a href="#reflect" class="header-anchor">#</a> Reflect</h1> <h2 id="概述"><a href="#概述" class="header-anchor">#</a> 概述</h2> <p><code>Reflect</code>对象与<code>Proxy</code>对象一样,也是 ES6 为了操作对象而提供的新 API。<code>Reflect</code>对象的设计目的有这样几个。</p> <p>(1) **将<code>Object</code>对象的一些明显属于语言内部的方法(比如<code>Object.defineProperty</code>),放到<code>Reflect</code>对象上。**现阶段,某些方法同时在<code>Object</code>和<code>Reflect</code>对象上部署,未来的新方法将只部署在<code>Reflect</code>对象上。也就是说,从<code>Reflect</code>对象上可以拿到语言内部的方法。
  25. (2) <strong>修改某些<code>Object</code>方法的返回结果,让其变得更合理</strong>。比如,<code>Object.defineProperty(obj, name, desc)</code>在无法定义属性时,会抛出一个错误,而<code>Reflect.defineProperty(obj, name, desc)</code>则会返回<code>false</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// 老写法</span>
  26. <span class="token keyword">try</span> <span class="token punctuation">{</span>
  27. Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> property<span class="token punctuation">,</span> attributes<span class="token punctuation">)</span><span class="token punctuation">;</span>
  28. <span class="token comment">// success</span>
  29. <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  30. <span class="token comment">// failure</span>
  31. <span class="token punctuation">}</span>
  32. <span class="token comment">// 新写法</span>
  33. <span class="token keyword">if</span> <span class="token punctuation">(</span>Reflect<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> property<span class="token punctuation">,</span> attributes<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  34. <span class="token comment">// success</span>
  35. <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
  36. <span class="token comment">// failure</span>
  37. <span class="token punctuation">}</span>
  38. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><p>(3) <strong>让<code>Object</code>操作都变成函数行为</strong>。某些<code>Object</code>操作是命令式,比如<code>name in obj</code>和<code>delete obj[name]</code>,而<code>Reflect.has(obj, name)</code>和<code>Reflect.deleteProperty(obj, name)</code>让它们变成了函数行为。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// 老写法</span>
  39. <span class="token string">'assign'</span> <span class="token keyword">in</span> Object <span class="token comment">// true</span>
  40. <span class="token comment">// 新写法</span>
  41. Reflect<span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span>Object<span class="token punctuation">,</span> <span class="token string">'assign'</span><span class="token punctuation">)</span> <span class="token comment">// true</span>
  42. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>(4)<code>Reflect</code>对象的方法与<code>Proxy</code>对象的方法一一对应,只要是<code>Proxy</code>对象的方法,就能在<code>Reflect</code>对象上找到对应的方法。这就让<code>Proxy</code>对象可以方便地调用对应的<code>Reflect</code>方法,完成默认行为,作为修改行为的基础。也就是说,<strong>不管<code>Proxy</code>怎么修改默认行为,你总可以在<code>Reflect</code>上获取默认行为</strong>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token function">Proxy</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> <span class="token punctuation">{</span>
  43. <span class="token function-variable function">set</span><span class="token operator">:</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> name<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  44. <span class="token keyword">var</span> success <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> name<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span><span class="token punctuation">;</span>
  45. <span class="token keyword">if</span> <span class="token punctuation">(</span>success<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  46. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'property '</span> <span class="token operator">+</span> name <span class="token operator">+</span> <span class="token string">' on '</span> <span class="token operator">+</span> target <span class="token operator">+</span> <span class="token string">' set to '</span> <span class="token operator">+</span> value<span class="token punctuation">)</span><span class="token punctuation">;</span>
  47. <span class="token punctuation">}</span>
  48. <span class="token keyword">return</span> success<span class="token punctuation">;</span>
  49. <span class="token punctuation">}</span>
  50. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  51. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>上面代码中,<code>Proxy</code>方法拦截<code>target</code>对象的属性赋值行为。它采用<code>Reflect.set</code>方法将值赋值给对象的属性,确保完成原有的行为,然后再部署额外的功能。</p> <p>下面是另一个例子。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> loggedObj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> <span class="token punctuation">{</span>
  52. <span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> name<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  53. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'get'</span><span class="token punctuation">,</span> target<span class="token punctuation">,</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
  54. <span class="token keyword">return</span> Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
  55. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  56. <span class="token function">deleteProperty</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> name</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  57. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'delete'</span> <span class="token operator">+</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
  58. <span class="token keyword">return</span> Reflect<span class="token punctuation">.</span><span class="token function">deleteProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
  59. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  60. <span class="token function">has</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> name</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  61. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'has'</span> <span class="token operator">+</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
  62. <span class="token keyword">return</span> Reflect<span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
  63. <span class="token punctuation">}</span>
  64. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  65. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><p>上面代码中,每一个<code>Proxy</code>对象的拦截操作(<code>get</code>、<code>delete</code>、<code>has</code>),内部都调用对应的<code>Reflect</code>方法,保证原生行为能够正常执行。添加的工作,就是将每一个操作输出一行日志。</p> <p>有了<code>Reflect</code>对象以后,很多操作会更易读。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// 老写法</span>
  66. <span class="token class-name">Function</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span>floor<span class="token punctuation">,</span> <span class="token keyword">undefined</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">1.75</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token comment">// 1</span>
  67. <span class="token comment">// 新写法</span>
  68. <span class="token function">Reflect</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span>floor<span class="token punctuation">,</span> <span class="token keyword">undefined</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token number">1.75</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token comment">// 1</span>
  69. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><h2 id="静态方法"><a href="#静态方法" class="header-anchor">#</a> 静态方法</h2> <p><code>Reflect</code>对象一共有 13 个静态方法。</p> <ul><li>Reflect.apply(target, thisArg, args)</li> <li>Reflect.construct(target, args)</li> <li>Reflect.get(target, name, receiver)</li> <li>Reflect.set(target, name, value, receiver)</li> <li>Reflect.defineProperty(target, name, desc)</li> <li>Reflect.deleteProperty(target, name)</li> <li>Reflect.has(target, name)</li> <li>Reflect.ownKeys(target)</li> <li>Reflect.isExtensible(target)</li> <li>Reflect.preventExtensions(target)</li> <li>Reflect.getOwnPropertyDescriptor(target, name)</li> <li>Reflect.getPrototypeOf(target)</li> <li>Reflect.setPrototypeOf(target, prototype)</li></ul> <p>上面这些方法的作用,大部分与<code>Object</code>对象的同名方法的作用都是相同的,而且它与<code>Proxy</code>对象的方法是一一对应的。下面是对它们的解释。</p> <h3 id="reflect-get-target-name-receiver"><a href="#reflect-get-target-name-receiver" class="header-anchor">#</a> Reflect.get(target, name, receiver)</h3> <p><code>Reflect.get</code>方法查找并返回<code>target</code>对象的<code>name</code>属性,如果没有该属性,则返回<code>undefined</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  70. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
  71. <span class="token literal-property property">bar</span><span class="token operator">:</span> <span class="token number">2</span><span class="token punctuation">,</span>
  72. <span class="token keyword">get</span> <span class="token function">baz</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  73. <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>foo <span class="token operator">+</span> <span class="token keyword">this</span><span class="token punctuation">.</span>bar<span class="token punctuation">;</span>
  74. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  75. <span class="token punctuation">}</span>
  76. Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token comment">// 1</span>
  77. Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'bar'</span><span class="token punctuation">)</span> <span class="token comment">// 2</span>
  78. Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'baz'</span><span class="token punctuation">)</span> <span class="token comment">// 3</span>
  79. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p>如果<code>name</code>属性部署了读取函数(getter),则读取函数的<code>this</code>绑定<code>receiver</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  80. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
  81. <span class="token literal-property property">bar</span><span class="token operator">:</span> <span class="token number">2</span><span class="token punctuation">,</span>
  82. <span class="token keyword">get</span> <span class="token function">baz</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  83. <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>foo <span class="token operator">+</span> <span class="token keyword">this</span><span class="token punctuation">.</span>bar<span class="token punctuation">;</span>
  84. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  85. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  86. <span class="token keyword">var</span> myReceiverObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  87. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">4</span><span class="token punctuation">,</span>
  88. <span class="token literal-property property">bar</span><span class="token operator">:</span> <span class="token number">4</span><span class="token punctuation">,</span>
  89. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  90. Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'baz'</span><span class="token punctuation">,</span> myReceiverObject<span class="token punctuation">)</span> <span class="token comment">// 8</span>
  91. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><p>如果第一个参数不是对象,<code>Reflect.get</code>方法会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  92. Reflect<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  93. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="reflect-set-target-name-value-receiver"><a href="#reflect-set-target-name-value-receiver" class="header-anchor">#</a> Reflect.set(target, name, value, receiver)</h3> <p><code>Reflect.set</code>方法设置<code>target</code>对象的<code>name</code>属性等于<code>value</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  94. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
  95. <span class="token keyword">set</span> <span class="token function">bar</span><span class="token punctuation">(</span><span class="token parameter">value</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  96. <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>foo <span class="token operator">=</span> value<span class="token punctuation">;</span>
  97. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  98. <span class="token punctuation">}</span>
  99. myObject<span class="token punctuation">.</span>foo <span class="token comment">// 1</span>
  100. Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  101. myObject<span class="token punctuation">.</span>foo <span class="token comment">// 2</span>
  102. Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'bar'</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span>
  103. myObject<span class="token punctuation">.</span>foo <span class="token comment">// 3</span>
  104. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><p>如果<code>name</code>属性设置了赋值函数,则赋值函数的<code>this</code>绑定<code>receiver</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  105. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">4</span><span class="token punctuation">,</span>
  106. <span class="token keyword">set</span> <span class="token function">bar</span><span class="token punctuation">(</span><span class="token parameter">value</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  107. <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>foo <span class="token operator">=</span> value<span class="token punctuation">;</span>
  108. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  109. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  110. <span class="token keyword">var</span> myReceiverObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  111. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">0</span><span class="token punctuation">,</span>
  112. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  113. Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'bar'</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> myReceiverObject<span class="token punctuation">)</span><span class="token punctuation">;</span>
  114. myObject<span class="token punctuation">.</span>foo <span class="token comment">// 4</span>
  115. myReceiverObject<span class="token punctuation">.</span>foo <span class="token comment">// 1</span>
  116. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><p>注意,如果 <code>Proxy</code>对象和 <code>Reflect</code>对象联合使用,前者拦截赋值操作,后者完成赋值的默认行为,而且传入了<code>receiver</code>,那么<code>Reflect.set</code>会触发<code>Proxy.defineProperty</code>拦截。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">let</span> p <span class="token operator">=</span> <span class="token punctuation">{</span>
  117. <span class="token literal-property property">a</span><span class="token operator">:</span> <span class="token string">'a'</span>
  118. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  119. <span class="token keyword">let</span> handler <span class="token operator">=</span> <span class="token punctuation">{</span>
  120. <span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  121. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'set'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  122. Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span>
  123. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  124. <span class="token function">defineProperty</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> attribute</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  125. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'defineProperty'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  126. Reflect<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> attribute<span class="token punctuation">)</span><span class="token punctuation">;</span>
  127. <span class="token punctuation">}</span>
  128. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  129. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span>p<span class="token punctuation">,</span> handler<span class="token punctuation">)</span><span class="token punctuation">;</span>
  130. obj<span class="token punctuation">.</span>a <span class="token operator">=</span> <span class="token string">'A'</span><span class="token punctuation">;</span>
  131. <span class="token comment">// set</span>
  132. <span class="token comment">// defineProperty</span>
  133. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br></div></div><p>上面代码中,<code>Proxy.set</code>拦截里面使用了<code>Reflect.set</code>,而且传入了<code>receiver</code>,导致触发<code>Proxy.defineProperty</code>拦截。这是因为<code>Proxy.set</code>的<code>receiver</code>参数总是指向当前的 <code>Proxy</code>实例(即上例的<code>obj</code>),而<code>Reflect.set</code>一旦传入<code>receiver</code>,就会将属性赋值到<code>receiver</code>上面(即<code>obj</code>),导致触发<code>defineProperty</code>拦截。如果<code>Reflect.set</code>没有传入<code>receiver</code>,那么就不会触发<code>defineProperty</code>拦截。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">let</span> p <span class="token operator">=</span> <span class="token punctuation">{</span>
  134. <span class="token literal-property property">a</span><span class="token operator">:</span> <span class="token string">'a'</span>
  135. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  136. <span class="token keyword">let</span> handler <span class="token operator">=</span> <span class="token punctuation">{</span>
  137. <span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  138. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'set'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  139. Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">)</span>
  140. <span class="token punctuation">}</span><span class="token punctuation">,</span>
  141. <span class="token function">defineProperty</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> attribute</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  142. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'defineProperty'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  143. Reflect<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> attribute<span class="token punctuation">)</span><span class="token punctuation">;</span>
  144. <span class="token punctuation">}</span>
  145. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  146. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span>p<span class="token punctuation">,</span> handler<span class="token punctuation">)</span><span class="token punctuation">;</span>
  147. obj<span class="token punctuation">.</span>a <span class="token operator">=</span> <span class="token string">'A'</span><span class="token punctuation">;</span>
  148. <span class="token comment">// set</span>
  149. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><p>如果第一个参数不是对象,<code>Reflect.set</code>会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  150. Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  151. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="reflect-has-obj-name"><a href="#reflect-has-obj-name" class="header-anchor">#</a> Reflect.has(obj, name)</h3> <p><code>Reflect.has</code>方法对应<code>name in obj</code>里面的<code>in</code>运算符。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  152. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
  153. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  154. <span class="token comment">// 旧写法</span>
  155. <span class="token string">'foo'</span> <span class="token keyword">in</span> myObject <span class="token comment">// true</span>
  156. <span class="token comment">// 新写法</span>
  157. Reflect<span class="token punctuation">.</span><span class="token function">has</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token comment">// true</span>
  158. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>如果<code>Reflect.has()</code>方法的第一个参数不是对象,会报错。</p> <h3 id="reflect-deleteproperty-obj-name"><a href="#reflect-deleteproperty-obj-name" class="header-anchor">#</a> Reflect.deleteProperty(obj, name)</h3> <p><code>Reflect.deleteProperty</code>方法等同于<code>delete obj[name]</code>,用于删除对象的属性。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> myObj <span class="token operator">=</span> <span class="token punctuation">{</span> <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token string">'bar'</span> <span class="token punctuation">}</span><span class="token punctuation">;</span>
  159. <span class="token comment">// 旧写法</span>
  160. <span class="token keyword">delete</span> myObj<span class="token punctuation">.</span>foo<span class="token punctuation">;</span>
  161. <span class="token comment">// 新写法</span>
  162. Reflect<span class="token punctuation">.</span><span class="token function">deleteProperty</span><span class="token punctuation">(</span>myObj<span class="token punctuation">,</span> <span class="token string">'foo'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  163. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>该方法返回一个布尔值。如果删除成功,或者被删除的属性不存在,返回<code>true</code>;删除失败,被删除的属性依然存在,返回<code>false</code>。</p> <p>如果<code>Reflect.deleteProperty()</code>方法的第一个参数不是对象,会报错。</p> <h3 id="reflect-construct-target-args"><a href="#reflect-construct-target-args" class="header-anchor">#</a> Reflect.construct(target, args)</h3> <p><code>Reflect.construct</code>方法等同于<code>new target(...args)</code>,这提供了一种不使用<code>new</code>,来调用构造函数的方法。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">Greeting</span><span class="token punctuation">(</span><span class="token parameter">name</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  164. <span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
  165. <span class="token punctuation">}</span>
  166. <span class="token comment">// new 的写法</span>
  167. <span class="token keyword">const</span> instance <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Greeting</span><span class="token punctuation">(</span><span class="token string">'张三'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  168. <span class="token comment">// Reflect.construct 的写法</span>
  169. <span class="token keyword">const</span> instance <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">construct</span><span class="token punctuation">(</span>Greeting<span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token string">'张三'</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  170. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>如果<code>Reflect.construct()</code>方法的第一个参数不是函数,会报错。</p> <h3 id="reflect-getprototypeof-obj"><a href="#reflect-getprototypeof-obj" class="header-anchor">#</a> Reflect.getPrototypeOf(obj)</h3> <p><code>Reflect.getPrototypeOf</code>方法用于读取对象的<code>__proto__</code>属性,对应<code>Object.getPrototypeOf(obj)</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> myObj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FancyThing</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  171. <span class="token comment">// 旧写法</span>
  172. Object<span class="token punctuation">.</span><span class="token function">getPrototypeOf</span><span class="token punctuation">(</span>myObj<span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token class-name">FancyThing</span><span class="token punctuation">.</span>prototype<span class="token punctuation">;</span>
  173. <span class="token comment">// 新写法</span>
  174. Reflect<span class="token punctuation">.</span><span class="token function">getPrototypeOf</span><span class="token punctuation">(</span>myObj<span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token class-name">FancyThing</span><span class="token punctuation">.</span>prototype<span class="token punctuation">;</span>
  175. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p><code>Reflect.getPrototypeOf</code>和<code>Object.getPrototypeOf</code>的一个区别是,如果参数不是对象,<code>Object.getPrototypeOf</code>会将这个参数转为对象,然后再运行,而<code>Reflect.getPrototypeOf</code>会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>Object<span class="token punctuation">.</span><span class="token function">getPrototypeOf</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">// Number {[[PrimitiveValue]]: 0}</span>
  176. Reflect<span class="token punctuation">.</span><span class="token function">getPrototypeOf</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  177. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="reflect-setprototypeof-obj-newproto"><a href="#reflect-setprototypeof-obj-newproto" class="header-anchor">#</a> Reflect.setPrototypeOf(obj, newProto)</h3> <p><code>Reflect.setPrototypeOf</code>方法用于设置目标对象的原型(prototype),对应<code>Object.setPrototypeOf(obj, newProto)</code>方法。它返回一个布尔值,表示是否设置成功。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> myObj <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
  178. <span class="token comment">// 旧写法</span>
  179. Object<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span>myObj<span class="token punctuation">,</span> <span class="token class-name">Array</span><span class="token punctuation">.</span>prototype<span class="token punctuation">)</span><span class="token punctuation">;</span>
  180. <span class="token comment">// 新写法</span>
  181. Reflect<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span>myObj<span class="token punctuation">,</span> <span class="token class-name">Array</span><span class="token punctuation">.</span>prototype<span class="token punctuation">)</span><span class="token punctuation">;</span>
  182. myObj<span class="token punctuation">.</span>length <span class="token comment">// 0</span>
  183. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>如果无法设置目标对象的原型(比如,目标对象禁止扩展),<code>Reflect.setPrototypeOf</code>方法返回<code>false</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>Reflect<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
  184. <span class="token comment">// true</span>
  185. Reflect<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span>Object<span class="token punctuation">.</span><span class="token function">freeze</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
  186. <span class="token comment">// false</span>
  187. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>如果第一个参数不是对象,<code>Object.setPrototypeOf</code>会返回第一个参数本身,而<code>Reflect.setPrototypeOf</code>会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>Object<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span>
  188. <span class="token comment">// 1</span>
  189. Reflect<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span>
  190. <span class="token comment">// TypeError: Reflect.setPrototypeOf called on non-object</span>
  191. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>如果第一个参数是<code>undefined</code>或<code>null</code>,<code>Object.setPrototypeOf</code>和<code>Reflect.setPrototypeOf</code>都会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>Object<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span>
  192. <span class="token comment">// TypeError: Object.setPrototypeOf called on null or undefined</span>
  193. Reflect<span class="token punctuation">.</span><span class="token function">setPrototypeOf</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span>
  194. <span class="token comment">// TypeError: Reflect.setPrototypeOf called on non-object</span>
  195. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><h3 id="reflect-apply-func-thisarg-args"><a href="#reflect-apply-func-thisarg-args" class="header-anchor">#</a> Reflect.apply(func, thisArg, args)</h3> <p><code>Reflect.apply</code>方法等同于<code>Function.prototype.apply.call(func, thisArg, args)</code>,用于绑定<code>this</code>对象后执行给定函数。</p> <p>一般来说,如果要绑定一个函数的<code>this</code>对象,可以这样写<code>fn.apply(obj, args)</code>,但是如果函数定义了自己的<code>apply</code>方法,就只能写成<code>Function.prototype.apply.call(fn, obj, args)</code>,采用<code>Reflect</code>对象可以简化这种操作。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> ages <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">11</span><span class="token punctuation">,</span> <span class="token number">33</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">54</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">,</span> <span class="token number">96</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
  196. <span class="token comment">// 旧写法</span>
  197. <span class="token keyword">const</span> youngest <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">min</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>Math<span class="token punctuation">,</span> ages<span class="token punctuation">)</span><span class="token punctuation">;</span>
  198. <span class="token keyword">const</span> oldest <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>Math<span class="token punctuation">,</span> ages<span class="token punctuation">)</span><span class="token punctuation">;</span>
  199. <span class="token keyword">const</span> type <span class="token operator">=</span> <span class="token class-name">Object</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>youngest<span class="token punctuation">)</span><span class="token punctuation">;</span>
  200. <span class="token comment">// 新写法</span>
  201. <span class="token keyword">const</span> youngest <span class="token operator">=</span> <span class="token function">Reflect</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span>min<span class="token punctuation">,</span> Math<span class="token punctuation">,</span> ages<span class="token punctuation">)</span><span class="token punctuation">;</span>
  202. <span class="token keyword">const</span> oldest <span class="token operator">=</span> <span class="token function">Reflect</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span>max<span class="token punctuation">,</span> Math<span class="token punctuation">,</span> ages<span class="token punctuation">)</span><span class="token punctuation">;</span>
  203. <span class="token keyword">const</span> type <span class="token operator">=</span> <span class="token function">Reflect</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token class-name">Object</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span>toString<span class="token punctuation">,</span> youngest<span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  204. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><h3 id="reflect-defineproperty-target-propertykey-attributes"><a href="#reflect-defineproperty-target-propertykey-attributes" class="header-anchor">#</a> Reflect.defineProperty(target, propertyKey, attributes)</h3> <p><code>Reflect.defineProperty</code>方法基本等同于<code>Object.defineProperty</code>,用来为对象定义属性。未来,后者会被逐渐废除,请从现在开始就使用<code>Reflect.defineProperty</code>代替它。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">MyDate</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  205. <span class="token comment">/*…*/</span>
  206. <span class="token punctuation">}</span>
  207. <span class="token comment">// 旧写法</span>
  208. Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>MyDate<span class="token punctuation">,</span> <span class="token string">'now'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
  209. <span class="token function-variable function">value</span><span class="token operator">:</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> Date<span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  210. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  211. <span class="token comment">// 新写法</span>
  212. Reflect<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>MyDate<span class="token punctuation">,</span> <span class="token string">'now'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
  213. <span class="token function-variable function">value</span><span class="token operator">:</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> Date<span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  214. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  215. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>如果<code>Reflect.defineProperty</code>的第一个参数不是对象,就会抛出错误,比如<code>Reflect.defineProperty(1, 'foo')</code>。</p> <p>这个方法可以与<code>Proxy.defineProperty</code>配合使用。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> p <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
  216. <span class="token function">defineProperty</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> prop<span class="token punctuation">,</span> descriptor</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  217. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>descriptor<span class="token punctuation">)</span><span class="token punctuation">;</span>
  218. <span class="token keyword">return</span> Reflect<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> prop<span class="token punctuation">,</span> descriptor<span class="token punctuation">)</span><span class="token punctuation">;</span>
  219. <span class="token punctuation">}</span>
  220. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  221. p<span class="token punctuation">.</span>foo <span class="token operator">=</span> <span class="token string">'bar'</span><span class="token punctuation">;</span>
  222. <span class="token comment">// {value: &quot;bar&quot;, writable: true, enumerable: true, configurable: true}</span>
  223. p<span class="token punctuation">.</span>foo <span class="token comment">// &quot;bar&quot;</span>
  224. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p>上面代码中,<code>Proxy.defineProperty</code>对属性赋值设置了拦截,然后使用<code>Reflect.defineProperty</code>完成了赋值。</p> <h3 id="reflect-getownpropertydescriptor-target-propertykey"><a href="#reflect-getownpropertydescriptor-target-propertykey" class="header-anchor">#</a> Reflect.getOwnPropertyDescriptor(target, propertyKey)</h3> <p><code>Reflect.getOwnPropertyDescriptor</code>基本等同于<code>Object.getOwnPropertyDescriptor</code>,用于得到指定属性的描述对象,将来会替代掉后者。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
  225. Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'hidden'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
  226. <span class="token literal-property property">value</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span>
  227. <span class="token literal-property property">enumerable</span><span class="token operator">:</span> <span class="token boolean">false</span><span class="token punctuation">,</span>
  228. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  229. <span class="token comment">// 旧写法</span>
  230. <span class="token keyword">var</span> theDescriptor <span class="token operator">=</span> Object<span class="token punctuation">.</span><span class="token function">getOwnPropertyDescriptor</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'hidden'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  231. <span class="token comment">// 新写法</span>
  232. <span class="token keyword">var</span> theDescriptor <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">getOwnPropertyDescriptor</span><span class="token punctuation">(</span>myObject<span class="token punctuation">,</span> <span class="token string">'hidden'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  233. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p><code>Reflect.getOwnPropertyDescriptor</code>和<code>Object.getOwnPropertyDescriptor</code>的一个区别是,如果第一个参数不是对象,<code>Object.getOwnPropertyDescriptor(1, 'foo')</code>不报错,返回<code>undefined</code>,而<code>Reflect.getOwnPropertyDescriptor(1, 'foo')</code>会抛出错误,表示参数非法。</p> <h3 id="reflect-isextensible-target"><a href="#reflect-isextensible-target" class="header-anchor">#</a> Reflect.isExtensible (target)</h3> <p><code>Reflect.isExtensible</code>方法对应<code>Object.isExtensible</code>,返回一个布尔值,表示当前对象是否可扩展。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
  234. <span class="token comment">// 旧写法</span>
  235. Object<span class="token punctuation">.</span><span class="token function">isExtensible</span><span class="token punctuation">(</span>myObject<span class="token punctuation">)</span> <span class="token comment">// true</span>
  236. <span class="token comment">// 新写法</span>
  237. Reflect<span class="token punctuation">.</span><span class="token function">isExtensible</span><span class="token punctuation">(</span>myObject<span class="token punctuation">)</span> <span class="token comment">// true</span>
  238. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>如果参数不是对象,<code>Object.isExtensible</code>会返回<code>false</code>,因为非对象本来就是不可扩展的,而<code>Reflect.isExtensible</code>会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>Object<span class="token punctuation">.</span><span class="token function">isExtensible</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">// false</span>
  239. Reflect<span class="token punctuation">.</span><span class="token function">isExtensible</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  240. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="reflect-preventextensions-target"><a href="#reflect-preventextensions-target" class="header-anchor">#</a> Reflect.preventExtensions(target)</h3> <p><code>Reflect.preventExtensions</code>对应<code>Object.preventExtensions</code>方法,用于让一个对象变为不可扩展。它返回一个布尔值,表示是否操作成功。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
  241. <span class="token comment">// 旧写法</span>
  242. Object<span class="token punctuation">.</span><span class="token function">preventExtensions</span><span class="token punctuation">(</span>myObject<span class="token punctuation">)</span> <span class="token comment">// Object {}</span>
  243. <span class="token comment">// 新写法</span>
  244. Reflect<span class="token punctuation">.</span><span class="token function">preventExtensions</span><span class="token punctuation">(</span>myObject<span class="token punctuation">)</span> <span class="token comment">// true</span>
  245. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>如果参数不是对象,<code>Object.preventExtensions</code>在 ES5 环境报错,在 ES6 环境返回传入的参数,而<code>Reflect.preventExtensions</code>会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// ES5 环境</span>
  246. Object<span class="token punctuation">.</span><span class="token function">preventExtensions</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  247. <span class="token comment">// ES6 环境</span>
  248. Object<span class="token punctuation">.</span><span class="token function">preventExtensions</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">// 1</span>
  249. <span class="token comment">// 新写法</span>
  250. Reflect<span class="token punctuation">.</span><span class="token function">preventExtensions</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token comment">// 报错</span>
  251. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><h3 id="reflect-ownkeys-target"><a href="#reflect-ownkeys-target" class="header-anchor">#</a> Reflect.ownKeys (target)</h3> <p><code>Reflect.ownKeys</code>方法用于返回对象的所有属性,基本等同于<code>Object.getOwnPropertyNames</code>与<code>Object.getOwnPropertySymbols</code>之和。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> myObject <span class="token operator">=</span> <span class="token punctuation">{</span>
  252. <span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
  253. <span class="token literal-property property">bar</span><span class="token operator">:</span> <span class="token number">2</span><span class="token punctuation">,</span>
  254. <span class="token punctuation">[</span>Symbol<span class="token punctuation">.</span><span class="token function">for</span><span class="token punctuation">(</span><span class="token string">'baz'</span><span class="token punctuation">)</span><span class="token punctuation">]</span><span class="token operator">:</span> <span class="token number">3</span><span class="token punctuation">,</span>
  255. <span class="token punctuation">[</span>Symbol<span class="token punctuation">.</span><span class="token function">for</span><span class="token punctuation">(</span><span class="token string">'bing'</span><span class="token punctuation">)</span><span class="token punctuation">]</span><span class="token operator">:</span> <span class="token number">4</span><span class="token punctuation">,</span>
  256. <span class="token punctuation">}</span><span class="token punctuation">;</span>
  257. <span class="token comment">// 旧写法</span>
  258. Object<span class="token punctuation">.</span><span class="token function">getOwnPropertyNames</span><span class="token punctuation">(</span>myObject<span class="token punctuation">)</span>
  259. <span class="token comment">// ['foo', 'bar']</span>
  260. Object<span class="token punctuation">.</span><span class="token function">getOwnPropertySymbols</span><span class="token punctuation">(</span>myObject<span class="token punctuation">)</span>
  261. <span class="token comment">//[Symbol(baz), Symbol(bing)]</span>
  262. <span class="token comment">// 新写法</span>
  263. Reflect<span class="token punctuation">.</span><span class="token function">ownKeys</span><span class="token punctuation">(</span>myObject<span class="token punctuation">)</span>
  264. <span class="token comment">// ['foo', 'bar', Symbol(baz), Symbol(bing)]</span>
  265. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br></div></div><p>如果<code>Reflect.ownKeys()</code>方法的第一个参数不是对象,会报错。</p> <h2 id="实例-使用-proxy-实现观察者模式"><a href="#实例-使用-proxy-实现观察者模式" class="header-anchor">#</a> 实例:使用 Proxy 实现观察者模式</h2> <p><strong>观察者模式(Observer mode)指的是函数自动观察数据对象,一旦对象有变化,函数就会自动执行</strong>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> person <span class="token operator">=</span> <span class="token function">observable</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  266. <span class="token literal-property property">name</span><span class="token operator">:</span> <span class="token string">'张三'</span><span class="token punctuation">,</span>
  267. <span class="token literal-property property">age</span><span class="token operator">:</span> <span class="token number">20</span>
  268. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 观察目标</span>
  269. <span class="token keyword">function</span> <span class="token function">print</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  270. console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>person<span class="token punctuation">.</span>name<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">, </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>person<span class="token punctuation">.</span>age<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
  271. <span class="token punctuation">}</span> <span class="token comment">// 观察者</span>
  272. <span class="token function">observe</span><span class="token punctuation">(</span>print<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 启动观察</span>
  273. person<span class="token punctuation">.</span>name <span class="token operator">=</span> <span class="token string">'李四'</span><span class="token punctuation">;</span>
  274. <span class="token comment">// 输出</span>
  275. <span class="token comment">// 李四, 20</span>
  276. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>上面代码中,数据对象<code>person</code>是观察目标,函数<code>print</code>是观察者。一旦数据对象发生变化,<code>print</code>就会自动执行。</p> <p>下面,使用 Proxy 写一个观察者模式的最简单实现,即实现<code>observable</code>和<code>observe</code>这两个函数。思路是<code>observable</code>函数返回一个原始对象的 Proxy 代理,拦截赋值操作,触发充当观察者的各个函数。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> queuedObservers <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Set</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  277. <span class="token keyword">const</span> <span class="token function-variable function">observe</span> <span class="token operator">=</span> <span class="token parameter">fn</span> <span class="token operator">=&gt;</span> queuedObservers<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>fn<span class="token punctuation">)</span><span class="token punctuation">;</span>
  278. <span class="token keyword">const</span> <span class="token function-variable function">observable</span> <span class="token operator">=</span> <span class="token parameter">obj</span> <span class="token operator">=&gt;</span> <span class="token keyword">new</span> <span class="token class-name">Proxy</span><span class="token punctuation">(</span>obj<span class="token punctuation">,</span> <span class="token punctuation">{</span>set<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  279. <span class="token keyword">function</span> <span class="token function">set</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  280. <span class="token keyword">const</span> result <span class="token operator">=</span> Reflect<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>target<span class="token punctuation">,</span> key<span class="token punctuation">,</span> value<span class="token punctuation">,</span> receiver<span class="token punctuation">)</span><span class="token punctuation">;</span>
  281. queuedObservers<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">observer</span> <span class="token operator">=&gt;</span> <span class="token function">observer</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  282. <span class="token keyword">return</span> result<span class="token punctuation">;</span>
  283. <span class="token punctuation">}</span>
  284. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p>上面代码中,先定义了一个<code>Set</code>集合,所有观察者函数都放进这个集合。然后,<code>observable</code>函数返回原始对象的代理,拦截赋值操作。拦截函数<code>set</code>之中,会自动执行所有观察者。</p></div></div> <div class="page-edit"><div class="edit-link"><a href="https://github.com/heBody/blog/edit/master/docs/《ES6 教程》笔记/15.Reflect.md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <div class="tags"><a href="/blog/tags/?tag=ES6" title="标签">#ES6</a></div> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2022/12/14, 19:36:42</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/blog/pages/f56ec2ab97d60483/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">Proxy</div></a> <a href="/blog/pages/2810ae8985e9bd52/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">Promise 对象</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
  285. <a href="/blog/pages/f56ec2ab97d60483/" class="prev">Proxy</a></span> <span class="next"><a href="/blog/pages/2810ae8985e9bd52/">Promise 对象</a>→
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