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noreferrer"}},[t._v("不可变对象"),s("OutboundLink")],1),t._v("。一旦被创建，你就无法更改它的子元素或者属性。一个元素就像电影的单帧：它代表了某个特定时刻的 UI。")]),t._v(" "),s("p",[t._v("根据我们已有的知识，更新 UI 唯一的方式是创建一个全新的元素，并将其传入 "),s("a",{attrs:{href:"https://zh-hans.reactjs.org/docs/react-dom.html#render",target:"_blank",rel:"noopener noreferrer"}},[s("code",[t._v("ReactDOM.render()")]),s("OutboundLink")],1),t._v("。")]),t._v(" "),s("p",[t._v("考虑一个计时器的例子：")]),t._v(" "),s("div",{staticClass:"language-jsx line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-jsx"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("tick")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// element是一个React元素")]),t._v("\n 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