(window.webpackJsonp=window.webpackJsonp||[]).push([[166],{493:function(s,t,a){"use strict";a.r(t);var n=a(3),e=Object(n.a)({},(function(){var s=this,t=s._self._c;return t("ContentSlotsDistributor",{attrs:{"slot-key":s.$parent.slotKey}},[t("h1",{attrs:{id:"类"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#类"}},[s._v("#")]),s._v(" 类")]),s._v(" "),t("p",[s._v("对于传统的 JavaScript 程序我们会使用函数和基于原型的继承来创建可重用的组件，但对于熟悉使用面向对象方式的程序员使用这些语法就有些棘手，因为他们用的是基于类的继承并且对象是由类构建出来的。 从 ECMAScript 2015，也就是 ES6 开始， JavaScript 程序员将能够使用基于类的面向对象的方式。 使用 TypeScript，我们允许开发者现在就使用这些特性，并且编译后的 JavaScript 可以在所有主流浏览器和平台上运行，而不需要等到下个 JavaScript 版本。")]),s._v(" "),t("h2",{attrs:{id:"基本示例"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#基本示例"}},[s._v("#")]),s._v(" 基本示例")]),s._v(" "),t("p",[s._v("下面看一个使用类的例子：")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" 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这一次，我们使用 "),t("code",[s._v("extends")]),s._v(" 关键字创建了 Animal的两个子类："),t("code",[s._v("Horse")]),s._v(" 和 "),t("code",[s._v("Snake")]),s._v("。")]),s._v(" "),t("p",[s._v("与前一个例子的不同点是，派生类包含了一个构造函数，它 必须调用 "),t("code",[s._v("super()")]),s._v("，它会执行基类的构造函数。 而且，在构造函数里访问 "),t("code",[s._v("this")]),s._v(" 的属性之前，我们 一定要调用 "),t("code",[s._v("super()")]),s._v("。 这个是 TypeScript 强制执行的一条重要规则。")]),s._v(" "),t("p",[s._v("这个例子演示了如何在子类里可以重写父类的方法。"),t("code",[s._v("Snake")]),s._v("类和 "),t("code",[s._v("Horse")]),s._v(" 类都创建了 "),t("code",[s._v("move")]),s._v(" 方法，它们重写了从 "),t("code",[s._v("Animal")]),s._v(" 继承来的 "),t("code",[s._v("move")]),s._v(" 方法，使得 "),t("code",[s._v("move")]),s._v(" 方法根据不同的类而具有不同的功能。注意，即使 "),t("code",[s._v("tom")]),s._v(" 被声明为 "),t("code",[s._v("Animal")]),s._v(" 类型，但因为它的值是 "),t("code",[s._v("Horse")]),s._v("，调用 "),t("code",[s._v("tom.move(34)")]),s._v(" 时，它会调用 "),t("code",[s._v("Horse")]),s._v(" 里重写的方法。")]),s._v(" "),t("div",{staticClass:"language- line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-text"}},[t("code",[s._v("Slithering...\nSammy moved 5m.\nGalloping...\nTommy moved 34m.\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br")])]),t("h2",{attrs:{id:"公共-私有与受保护的修饰符"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#公共-私有与受保护的修饰符"}},[s._v("#")]),s._v(" 公共，私有与受保护的修饰符")]),s._v(" "),t("h3",{attrs:{id:"默认为-public"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#默认为-public"}},[s._v("#")]),s._v(" 默认为 public")]),s._v(" "),t("p",[s._v("在上面的例子里，我们可以自由的访问程序里定义的成员。 如果你对其它语言中的类比较了解，就会注意到我们在之前的代码里并没有使用 "),t("code",[s._v("public")]),s._v(" 来做修饰；例如，C# 要求必须明确地使用 "),t("code",[s._v("public")]),s._v(" 指定成员是可见的。 在 TypeScript 里，成员都默认为 "),t("code",[s._v("public")]),s._v("。")]),s._v(" "),t("p",[s._v("你也可以明确的将一个成员标记成 "),t("code",[s._v("public")]),s._v("。 我们可以用下面的方式来重写上面的 "),t("code",[s._v("Animal")]),s._v(" 类：")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token 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keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" name\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Cat'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 错误: 'name' 是私有的.")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("TypeScript 使用的是结构性类型系统。 当我们比较两种不同的类型时，并不在乎它们从何处而来，如果所有成员的类型都是兼容的，我们就认为它们的类型是兼容的。")]),s._v(" "),t("p",[s._v("然而，当我们比较带有 "),t("code",[s._v("private")]),s._v(" 或 "),t("code",[s._v("protected")]),s._v(" 成员的类型的时候，情况就不同了。 如果其中一个类型里包含一个 "),t("code",[s._v("private")]),s._v(" 成员，那么只有当另外一个类型中也存在这样一个 "),t("code",[s._v("private")]),s._v(" 成员，并且它们都是来自同一处声明时，我们才认为这两个类型是兼容的。 对于 "),t("code",[s._v("protected")]),s._v(" 成员也使用这个规则。")]),s._v(" "),t("p",[s._v("下面来看一个例子，更好地说明了这一点：")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" name\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Rhino")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("super")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Rhino'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Employee")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" name\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" animal "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Goat'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" rhino "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Rhino")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" employee "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Employee")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Bob'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n\nanimal "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" rhino\nanimal "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" employee "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 错误: Animal 与 Employee 不兼容.")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br"),t("span",{staticClass:"line-number"},[s._v("16")]),t("br"),t("span",{staticClass:"line-number"},[s._v("17")]),t("br"),t("span",{staticClass:"line-number"},[s._v("18")]),t("br"),t("span",{staticClass:"line-number"},[s._v("19")]),t("br"),t("span",{staticClass:"line-number"},[s._v("20")]),t("br"),t("span",{staticClass:"line-number"},[s._v("21")]),t("br"),t("span",{staticClass:"line-number"},[s._v("22")]),t("br"),t("span",{staticClass:"line-number"},[s._v("23")]),t("br"),t("span",{staticClass:"line-number"},[s._v("24")]),t("br"),t("span",{staticClass:"line-number"},[s._v("25")]),t("br"),t("span",{staticClass:"line-number"},[s._v("26")]),t("br")])]),t("p",[s._v("这个例子中有 "),t("code",[s._v("Animal")]),s._v(" 和 "),t("code",[s._v("Rhino")]),s._v(" 两个类， "),t("code",[s._v("Rhino")]),s._v(" 是 "),t("code",[s._v("Animal")]),s._v(" 类的子类。 还有一个 "),t("code",[s._v("Employee")]),s._v(" 类，其类型看上去与 "),t("code",[s._v("Animal")]),s._v(" 是相同的。 我们创建了几个这些类的实例，并相互赋值来看看会发生什么。 因为 "),t("code",[s._v("Animal")]),s._v(" 和 "),t("code",[s._v("Rhino")]),s._v(" 共享了来自 "),t("code",[s._v("Animal")]),s._v(" 里的私有成员定义 "),t("code",[s._v("private name: string")]),s._v("，因此它们是兼容的。然而 "),t("code",[s._v("Employee")]),s._v(" 却不是这样。当把 "),t("code",[s._v("Employee")]),s._v(" 赋值给 "),t("code",[s._v("Animal")]),s._v(" 的时候，得到一个错误，说它们的类型不兼容。尽管 "),t("code",[s._v("Employee")]),s._v(" 里也有一个私有成员 "),t("code",[s._v("name")]),s._v("，但它明显不是 "),t("code",[s._v("Animal")]),s._v(" 里面定义的那个。")]),s._v(" "),t("h3",{attrs:{id:"理解-protected"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#理解-protected"}},[s._v("#")]),s._v(" 理解 protected")]),s._v(" "),t("p",[t("code",[s._v("protected")]),s._v(" 修饰符与 "),t("code",[s._v("private")]),s._v(" 修饰符的行为很相似，但有一点不同，"),t("code",[s._v("protected")]),s._v("成员在派生类中仍然可以访问。例如：")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("protected")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" name\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Employee")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" department"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" department"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("super")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("department "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" department\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getElevatorPitch")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token template-string"}},[t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("Hello, my name is ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(" and I work in ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("department"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")])]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" howard "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Employee")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Howard'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Sales'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("console")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("howard"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getElevatorPitch")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("console")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("howard"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// error")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br"),t("span",{staticClass:"line-number"},[s._v("16")]),t("br"),t("span",{staticClass:"line-number"},[s._v("17")]),t("br"),t("span",{staticClass:"line-number"},[s._v("18")]),t("br"),t("span",{staticClass:"line-number"},[s._v("19")]),t("br"),t("span",{staticClass:"line-number"},[s._v("20")]),t("br"),t("span",{staticClass:"line-number"},[s._v("21")]),t("br"),t("span",{staticClass:"line-number"},[s._v("22")]),t("br"),t("span",{staticClass:"line-number"},[s._v("23")]),t("br")])]),t("p",[s._v("注意，我们不能在 "),t("code",[s._v("Person")]),s._v(" 类外使用 "),t("code",[s._v("name")]),s._v("，但是我们仍然可以通过 "),t("code",[s._v("Employee")]),s._v(" 类的实例方法访问，因为 "),t("code",[s._v("Employee")]),s._v(" 是由 "),t("code",[s._v("Person")]),s._v("  派生而来的。")]),s._v(" "),t("p",[s._v("构造函数也可以被标记成 "),t("code",[s._v("protected")]),s._v("。 这意味着这个类不能在包含它的类外被实例化，但是能被继承。比如：")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("protected")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("protected")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" name\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Employee 能够继承 Person")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Employee")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" department"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" department"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("super")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("department "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" department\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getElevatorPitch")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token template-string"}},[t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("Hello, my name is ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(" and I work in ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("department"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")])]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" howard "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Employee")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Howard'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Sales'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" john "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'John'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 错误: 'Person' 的构造函数是被保护的.")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br"),t("span",{staticClass:"line-number"},[s._v("16")]),t("br"),t("span",{staticClass:"line-number"},[s._v("17")]),t("br"),t("span",{staticClass:"line-number"},[s._v("18")]),t("br"),t("span",{staticClass:"line-number"},[s._v("19")]),t("br"),t("span",{staticClass:"line-number"},[s._v("20")]),t("br"),t("span",{staticClass:"line-number"},[s._v("21")]),t("br"),t("span",{staticClass:"line-number"},[s._v("22")]),t("br"),t("span",{staticClass:"line-number"},[s._v("23")]),t("br")])]),t("h2",{attrs:{id:"readonly-修饰符"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#readonly-修饰符"}},[s._v("#")]),s._v(" readonly 修饰符")]),s._v(" "),t("p",[s._v("你可以使用 "),t("code",[s._v("readonly")]),s._v(" 关键字将属性设置为只读的。 只读属性必须在声明时或构造函数里被初始化。")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("readonly")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" name\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" john "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'John'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\njohn"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("name "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'peter'")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br")])]),t("h3",{attrs:{id:"参数属性"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#参数属性"}},[s._v("#")]),s._v(" 参数属性")]),s._v(" "),t("p",[s._v("在上面的例子中，我们必须在 "),t("code",[s._v("Person")]),s._v(" 类里定义一个只读成员 "),t("code",[s._v("name")]),s._v(" 和一个参数为 "),t("code",[s._v("name")]),s._v(" 的构造函数，并且立刻将 "),t("code",[s._v("name")]),s._v(" 的值赋给 "),t("code",[s._v("this.name")]),s._v("，这种情况经常会遇到。 参数属性可以方便地让我们在一个地方定义并初始化一个成员。 下面的例子是对之前 "),t("code",[s._v("Person")]),s._v(" 类的修改版，使用了参数属性：")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Person")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("constructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("readonly")]),s._v(" name"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br")])]),t("p",[s._v("注意看我们是如何舍弃参数 "),t("code",[s._v("name")]),s._v("，仅在构造函数里使用 "),t("code",[s._v("readonly name: string")]),s._v(" 参数来创建和初始化 "),t("code",[s._v("name")]),s._v(" 成员。 我们把声明和赋值合并至一处。")]),s._v(" "),t("p",[s._v("参数属性通过给构造函数参数前面添加一个访问限定符来声明。使用 "),t("code",[s._v("private")]),s._v(" 限定一个参数属性会声明并初始化一个私有成员；对于 "),t("code",[s._v("public")]),s._v(" 和 "),t("code",[s._v("protected")]),s._v(" 来说也是一样。")]),s._v(" "),t("h2",{attrs:{id:"存取器"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#存取器"}},[s._v("#")]),s._v(" 存取器")]),s._v(" "),t("p",[t("code",[s._v("TypeScript")]),s._v(" 支持通过 "),t("code",[s._v("getters/setters")]),s._v(" 来截取对对象成员的访问。 它能帮助你有效的控制对对象成员的访问。")]),s._v(" "),t("p",[s._v("下面来看如何把一个简单的类改写成使用 "),t("code",[s._v("get")]),s._v(" 和 "),t("code",[s._v("set")]),s._v("。 首先，我们从一个没有使用存取器的例子开始。")]),s._v(" "),t("div",{staticClass:"language-typescript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-typescript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Employee")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  fullName"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token builtin"}},[s._v("string")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" employee "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" 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