How the "Use Client" directive works in Next.js 13
<p>I'm trying to learn about server-side rendering using Next.js 13.4 and the new <code>app/</code> directory. From what I understand, every component is a <em>server</em> component by default (i.e. rendered on the server side). </p>
<p>However, we can use the <code>'use client'</code> directive to force the component to become an <em>client</em> component. </p>
<p>Below, I've set up a simple "Hello World" component, first as a server component and then as a client component. In each case, I compare the page source code.</p>
<h3><code>src/app/page.js</code>（服务器组件）</h3>
<pre class="brush:php;toolbar:false;">export default function Home() {
return (
<main>
<h1>Hello World</h1>
</main>
)
}</pre>
<p>Chrome > 查看页面源代码</p>
<pre class="brush:php;toolbar:false;"><!DOCTYPE html>
<html lang="en">
<head>
<meta charSet="utf-8" />
<title>Create Next App</title>
<meta name="description" content="Generated by create next app" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<script src="/_next/static/chunks/polyfills.js" noModule=""></script>
</head>
<body>
<main>
<h1>Hello World</h1>
</main>
<script src="/_next/static/chunks/webpack.js" async=""></script>
<script src="/_next/static/chunks/main-app.js" async=""></script>
<script>(self.__next_f = self.__next_f || []).push([0])</script>
<script>self.__next_f.push([1, "0:"$L1"n"])</script>
<script>self.__next_f.push([1, "2:I{"id":"(app-client)/./node_modules/next/dist/client/components/app-router.js","chunks":["webpack:static/chunks/webpack.js"],"name":"","async":false}n4:I{"id":"(app-client)/./node_modules/next/dist/client/components/error-boundary.js","chunks":["webpack:static/chunks/webpack.js"],"name":"","async":false}n6:I{"id":"(app-client)/./node_modules/next/dist/client/components/layout-router.js","chunks":["app-client-internals:static/chunks/app-client-internals.js"],"name":"","async":false}n7:I{"id":"(app-client)/"])</script>
<script>self.__next_f.push([1, "./node_modules/next/dist/client/components/render-from-template-context.js","chunks":["app-client-internals:static/chunks/app-client-internals.js"],"name":"","async":false}n"])</script>
<script>self.__next_f.push([1, "1:[[],["$","$L2",null,{"assetPrefix":"","initialCanonicalUrl":"/","initialTree":["",{"children":["__PAGE__",{}]},"$undefined","$undefined",true],"initialHead":["$L3",null],"globalErrorComponent":"$4","notFound":["$","html",null,{"lang":"en","children":["$","body",null,{"children":["$L5","$undefined",[["$","title",null,{"children":"404: This page could not be found."}],["$","div",null,{"style":{"fontFamily":"system-ui,\"Segoe UI\",Roboto,Helvetica,Arial,sans-serif,\"Apple Color Emoji\",\"Segoe UI Emoji\"","height":"100vh","textAlign":"center","display":"flex","flexDirection":"column","alignItems":"center","justifyContent":"center"},"children":["$","div",null,{"children":[["$","style",null,{"dangerouslySetInnerHTML":{"__html":"body{color:#000;background:#fff;margin:0}.next-error-h1{border-right:1px solid rgba(0,0,0,.3)}@media (prefers-color-scheme:dark){body{color:#fff;background:#000}.next-error-h1{border-right:1px solid rgba(255,255,255,.3)}}"}}],["$","h1",null,{"className":"next-error-h1","style":{"display":"inline-block","margin":"0 20px 0 0","padding":"0 23px 0 0","fontSize":24,"fontWeight":500,"verticalAlign":"top","lineHeight":"49px"},"children":"404"}],["$","div",null,{"style":{"display":"inline-block"},"children":["$","h2",null,{"style":{"fontSize":14,"fontWeight":400,"lineHeight":"49px","margin":0},"children":"This page could not be found."}]}]]}]}]]]}]}],"asNotFound":false,"children":[["$","html",null,{"lang":"en","children":["$","body",null,{"children":["$","$L6",null,{"parallelRouterKey":"children","segmentPath":["children"],"error":"$undefined","errorStyles":"$undefined","loading":"$undefined","loadingStyles":"$undefined","hasLoading":false,"template":["$","$L7",null,{}],"templateStyles":"$undefined","notFound":"$undefined","notFoundStyles":"$undefined","childProp":{"current":[["$","main",null,{"children":["$","h1",null,{"children":"Hello World"}]}],null],"segment":"__PAGE__"},"styles":[]}]}]}],null]}]]n"])</script>
<script>self.__next_f.push([1, "5:[[["$","meta",null,{"charSet":"utf-8"}],null,null,null,null,null,null,null,null,null,null,["$","meta",null,{"name":"viewport","content":"width=device-width, initial-scale=1"}],null,null,null,null,null,null,null,null,null,null,[]],[null,null,null,null],null,null,[null,null,null,null,null],null,null,null,null,null]n3:[[["$","meta",null,{"charSet":"utf-8"}],["$","title",null,{"children":"Create Next App"}],["$","meta",null,{"name":"description","content":"Generated by create next app"}],null,null,null,null,n"])</script>
<script>self.__next_f.push([1, "ull,null,null,null,["$","meta",null,{"name":"viewport","content":"width=device-width, initial-scale=1"}],null,null,null,null,null,null,null,null,null,null,[]],[null,null,null,null],null,null,[null,null,null,null,null],null,null,null,null,null]n"])</script>
</body>
</html></pre>
<h3><code>src/app/page.js</code>（客户端组件）</h3>
<pre class="brush:php;toolbar:false;">'use client';
export default function Home() {
return (
<main>
<h1>Hello World</h1>
</main>
)
}</pre>
<p>Chrome > 查看页面源代码</p>
<pre class="brush:php;toolbar:false;"><!DOCTYPE html>
<html lang="en">
<head>
<meta charSet="utf-8" />
<title>Create Next App</title>
<meta name="description" content="Generated by create next app" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<script src="/_next/static/chunks/polyfills.js" noModule=""></script>
</head>
<body>
<main>
<h1>Hello World</h1>
</main>
<script src="/_next/static/chunks/webpack.js" async=""></script>
<script src="/_next/static/chunks/main-app.js" async=""></script>
<script>(self.__next_f = self.__next_f || []).push([0])</script>
<script>self.__next_f.push([1, "0:"$L1"n"])</script>
<script>self.__next_f.push([1, "2:I{"id":"(app-client)/./node_modules/next/dist/client/components/app-router.js","chunks":["webpack:static/chunks/webpack.js"],"name":"","async":false}n4:I{"id":"(app-client)/./node_modules/next/dist/client/components/error-boundary.js","chunks":["webpack:static/chunks/webpack.js"],"name":"","async":false}n6:I{"id":"(app-client)/./node_modules/next/dist/client/components/layout-router.js","chunks":["app-client-internals:static/chunks/app-client-internals.js"],"name":"","async":false}n7:I{"id":"(app-client)/"])</script>
<script>self.__next_f.push([1, "./node_modules/next/dist/client/components/render-from-template-context.js","chunks":["app-client-internals:static/chunks/app-client-internals.js"],"name":"","async":false}n8:I{"id":"(app-client)/./src/app/page.js","chunks":["app/page:static/chunks/app/page.js"],"name":"","async":false}n"])</script>
<script>self.__next_f.push([1, "1:[[],["$","$L2",null,{"assetPrefix":"","initialCanonicalUrl":"/","initialTree":["",{"children":["__PAGE__",{}]},"$undefined","$undefined",true],"initialHead":["$L3",null],"globalErrorComponent":"$4","notFound":["$","html",null,{"lang":"en","children":["$","body",null,{"children":["$L5","$undefined",[["$","title",null,{"children":"404: This page could not be found."}],["$","div",null,{"style":{"fontFamily":"system-ui,\"Segoe UI\",Roboto,Helvetica,Arial,sans-serif,\"Apple Color Emoji\",\"Segoe UI Emoji\"","height":"100vh","textAlign":"center","display":"flex","flexDirection":"column","alignItems":"center","justifyContent":"center"},"children":["$","div",null,{"children":[["$","style",null,{"dangerouslySetInnerHTML":{"__html":"body{color:#000;background:#fff;margin:0}.next-error-h1{border-right:1px solid rgba(0,0,0,.3)}@media (prefers-color-scheme:dark){body{color:#fff;background:#000}.next-error-h1{border-right:1px solid rgba(255,255,255,.3)}}"}}],["$","h1",null,{"className":"next-error-h1","style":{"display":"inline-block","margin":"0 20px 0 0","padding":"0 23px 0 0","fontSize":24,"fontWeight":500,"verticalAlign":"top","lineHeight":"49px"},"children":"404"}],["$","div",null,{"style":{"display":"inline-block"},"children":["$","h2",null,{"style":{"fontSize":14,"fontWeight":400,"lineHeight":"49px","margin":0},"children":"This page could not be found."}]}]]}]}]]]}]}],"asNotFound":false,"children":[["$","html",null,{"lang":"en","children":["$","body",null,{"children":["$","$L6",null,{"parallelRouterKey":"children","segmentPath":["children"],"error":"$undefined","errorStyles":"$undefined","loading":"$undefined","loadingStyles":"$undefined","hasLoading":false,"template":["$","$L7",null,{}],"templateStyles":"$undefined","notFound":"$undefined","notFoundStyles":"$undefined","childProp":{"current":[["$","$L8",null,{"params":{},"searchParams":{}}],null],"segment":"__PAGE__"},"styles":[]}]}]}],null]}]]n"])</script>
<script>self.__next_f.push([1, "5:[[["$","meta",null,{"charSet":"utf-8"}],null,null,null,null,null,null,null,null,null,null,["$","meta",null,{"name":"viewport","content":"width=device-width, initial-scale=1"}],null,null,null,null,null,null,null,null,null,null,[]],[null,null,null,null],null,null,[null,null,null,null,null],null,null,null,null,null]n3:[[["$","meta",null,{"charSet":"utf-8"}],["$","title",null,{"children":"Create Next App"}],["$","meta",null,{"name":"description","content":"Generated by create next app"}],null,null,null,null,n"])</script>
<script>self.__next_f.push([1, "ull,null,null,null,["$","meta",null,{"name":"viewport","content":"width=device-width, initial-scale=1"}],null,null,null,null,null,null,null,null,null,null,[]],[null,null,null,null],null,null,[null,null,null,null,null],null,null,null,null,null]n"])</script>
</body>
</html></pre>
<hr />
<p>我很困惑，因为客户端组件似乎已预渲染了 HTML，但“Hello World”显然存在于源代码中。我期望看到类似于 React 根 DOM 节点的东西 - 基本上是一个空的 div 等待注入一些 HTML。我在这里缺少什么？</p>
