mirror of
https://github.com/facebook/react.git
synced 2025-11-01 09:12:30 +00:00
Dan Abramov
626 lines
35 KiB
HTML
626 lines
35 KiB
HTML
|
|
|
|
<!DOCTYPE html>
|
|
<!--[if IE]><![endif]-->
|
|
<html>
|
|
<head>
|
|
<meta charset="utf-8">
|
|
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
|
|
<title>Components and Props - React</title>
|
|
<meta name="viewport" content="width=device-width, initial-scale=1">
|
|
<meta property="og:title" content="Components and Props - React">
|
|
<meta property="og:type" content="website">
|
|
<meta property="og:url" content="https://facebook.github.io/react/docs/components-and-props.html">
|
|
<meta property="og:image" content="https://facebook.github.io/react/img/logo_og.png">
|
|
<meta property="og:description" content="A JavaScript library for building user interfaces">
|
|
<meta property="fb:app_id" content="623268441017527">
|
|
|
|
<link rel="shortcut icon" href="/react/favicon.ico">
|
|
<link rel="alternate" type="application/rss+xml" title="React" href="https://facebook.github.io/react/feed.xml">
|
|
|
|
<link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css" />
|
|
<link rel="stylesheet" href="/react/css/syntax.css">
|
|
<link rel="stylesheet" href="/react/css/codemirror.css">
|
|
<link rel="stylesheet" href="/react/css/react.css">
|
|
|
|
<script src="//use.typekit.net/vqa1hcx.js"></script>
|
|
<script>try{Typekit.load();}catch(e){}</script>
|
|
|
|
<!--[if lte IE 8]>
|
|
<script src="https://unpkg.com/html5shiv@3.7.3/dist/html5shiv.min.js"></script>
|
|
<script src="https://unpkg.com/es5-shim@4.5.9/es5-shim.min.js"></script>
|
|
<script src="https://unpkg.com/es5-shim@4.5.9/es5-sham.min.js"></script>
|
|
<![endif]-->
|
|
<script src="https://unpkg.com/docsearch.js@1.5.0/dist/cdn/docsearch.min.js"></script>
|
|
<script src="https://unpkg.com/codemirror@5.15.2"></script>
|
|
<script src="https://unpkg.com/codemirror@5.15.2/mode/javascript/javascript.js"></script>
|
|
<script src="https://unpkg.com/codemirror@5.15.2/mode/xml/xml.js"></script>
|
|
<script src="https://unpkg.com/codemirror@5.15.2/mode/jsx/jsx.js"></script>
|
|
<script src="https://unpkg.com/prop-types/prop-types.min.js"></script>
|
|
<script src="https://unpkg.com/react/umd/react.production.min.js"></script>
|
|
<script src="https://unpkg.com/react-dom/umd/react-dom.production.min.js"></script>
|
|
<script src="https://unpkg.com/create-react-class/create-react-class.min.js"></script>
|
|
<script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>
|
|
<script src="/react/js/live_editor.js"></script>
|
|
</head>
|
|
<body>
|
|
|
|
<div class="container">
|
|
|
|
<div class="nav-main">
|
|
<div class="wrap">
|
|
<a class="nav-home" href="/react/">
|
|
<img class="nav-logo" src="/react/img/logo.svg" width="36" height="36">
|
|
React
|
|
</a>
|
|
<div class="nav-lists">
|
|
<ul class="nav-site nav-site-internal">
|
|
<li><a href="/react/docs/hello-world.html" class="active">Docs</a></li>
|
|
<li><a href="/react/tutorial/tutorial.html">Tutorial</a></li>
|
|
<li><a href="/react/community/support.html">Community</a></li>
|
|
<li><a href="/react/blog/">Blog</a></li>
|
|
<li class="nav-site-search">
|
|
<input id="algolia-doc-search" type="text" placeholder="Search docs..." />
|
|
</li>
|
|
</ul>
|
|
<ul class="nav-site nav-site-external">
|
|
<li><a href="https://github.com/facebook/react">GitHub</a></li>
|
|
<li><a href="https://github.com/facebook/react/releases">v16.0.0</a></li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<section class="content wrap documentationContent">
|
|
<div class="inner-content">
|
|
<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/components-and-props.md" target="_blank">Edit on GitHub</a>
|
|
<h1>
|
|
Components and Props
|
|
</h1>
|
|
<div class="subHeader"></div>
|
|
|
|
<p>Components let you split the UI into independent, reusable pieces, and think about each piece in isolation.</p>
|
|
|
|
<p>Conceptually, components are like JavaScript functions. They accept arbitrary inputs (called "props") and return React elements describing what should appear on the screen.</p>
|
|
|
|
<h2>Functional and Class Components</h2>
|
|
|
|
<p>The simplest way to define a component is to write a JavaScript function:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">Welcome</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="o"><</span><span class="nx">h1</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span><span class="o"><</span><span class="err">/h1>;</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p>This function is a valid React component because it accepts a single "props" object argument with data and returns a React element. We call such components "functional" because they are literally JavaScript functions.</p>
|
|
|
|
<p>You can also use an <a href="https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Classes">ES6 class</a> to define a component:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kr">class</span> <span class="nx">Welcome</span> <span class="kr">extends</span> <span class="nx">React</span><span class="p">.</span><span class="nx">Component</span> <span class="p">{</span>
|
|
<span class="nx">render</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="o"><</span><span class="nx">h1</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span><span class="o"><</span><span class="err">/h1>;</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p>The above two components are equivalent from React's point of view.</p>
|
|
|
|
<p>Classes have some additional features that we will discuss in the <a href="/react/docs/state-and-lifecycle.html">next sections</a>. Until then, we will use functional components for their conciseness.</p>
|
|
|
|
<h2>Rendering a Component</h2>
|
|
|
|
<p>Previously, we only encountered React elements that represent DOM tags:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kr">const</span> <span class="nx">element</span> <span class="o">=</span> <span class="o"><</span><span class="nx">div</span> <span class="o">/></span><span class="p">;</span>
|
|
</code></pre></div>
|
|
<p>However, elements can also represent user-defined components:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kr">const</span> <span class="nx">element</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Welcome</span> <span class="nx">name</span><span class="o">=</span><span class="s2">"Sara"</span> <span class="o">/></span><span class="p">;</span>
|
|
</code></pre></div>
|
|
<p>When React sees an element representing a user-defined component, it passes JSX attributes to this component as a single object. We call this object "props".</p>
|
|
|
|
<p>For example, this code renders "Hello, Sara" on the page:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="hll"><span class="kd">function</span> <span class="nx">Welcome</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
</span> <span class="k">return</span> <span class="o"><</span><span class="nx">h1</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span><span class="o"><</span><span class="err">/h1>;</span>
|
|
<span class="p">}</span>
|
|
|
|
<span class="hll"><span class="kr">const</span> <span class="nx">element</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Welcome</span> <span class="nx">name</span><span class="o">=</span><span class="s2">"Sara"</span> <span class="o">/></span><span class="p">;</span>
|
|
</span><span class="nx">ReactDOM</span><span class="p">.</span><span class="nx">render</span><span class="p">(</span>
|
|
<span class="nx">element</span><span class="p">,</span>
|
|
<span class="nb">document</span><span class="p">.</span><span class="nx">getElementById</span><span class="p">(</span><span class="s1">'root'</span><span class="p">)</span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p><a href="http://codepen.io/gaearon/pen/YGYmEG?editors=0010">Try it on CodePen.</a></p>
|
|
|
|
<p>Let's recap what happens in this example:</p>
|
|
|
|
<ol>
|
|
<li>We call <code>ReactDOM.render()</code> with the <code><Welcome name="Sara" /></code> element.</li>
|
|
<li>React calls the <code>Welcome</code> component with <code>{name: 'Sara'}</code> as the props.</li>
|
|
<li>Our <code>Welcome</code> component returns a <code><h1>Hello, Sara</h1></code> element as the result.</li>
|
|
<li>React DOM efficiently updates the DOM to match <code><h1>Hello, Sara</h1></code>.</li>
|
|
</ol>
|
|
|
|
<blockquote>
|
|
<p><strong>Caveat:</strong></p>
|
|
|
|
<p>Always start component names with a capital letter.</p>
|
|
|
|
<p>For example, <code><div /></code> represents a DOM tag, but <code><Welcome /></code> represents a component and requires <code>Welcome</code> to be in scope.</p>
|
|
</blockquote>
|
|
|
|
<h2>Composing Components</h2>
|
|
|
|
<p>Components can refer to other components in their output. This lets us use the same component abstraction for any level of detail. A button, a form, a dialog, a screen: in React apps, all those are commonly expressed as components.</p>
|
|
|
|
<p>For example, we can create an <code>App</code> component that renders <code>Welcome</code> many times:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">Welcome</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="o"><</span><span class="nx">h1</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span><span class="o"><</span><span class="err">/h1>;</span>
|
|
<span class="p">}</span>
|
|
|
|
<span class="kd">function</span> <span class="nx">App</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">div</span><span class="o">></span>
|
|
<span class="hll"> <span class="o"><</span><span class="nx">Welcome</span> <span class="nx">name</span><span class="o">=</span><span class="s2">"Sara"</span> <span class="o">/></span>
|
|
</span><span class="hll"> <span class="o"><</span><span class="nx">Welcome</span> <span class="nx">name</span><span class="o">=</span><span class="s2">"Cahal"</span> <span class="o">/></span>
|
|
</span><span class="hll"> <span class="o"><</span><span class="nx">Welcome</span> <span class="nx">name</span><span class="o">=</span><span class="s2">"Edite"</span> <span class="o">/></span>
|
|
</span> <span class="o"><</span><span class="err">/div></span>
|
|
<span class="p">);</span>
|
|
<span class="p">}</span>
|
|
|
|
<span class="nx">ReactDOM</span><span class="p">.</span><span class="nx">render</span><span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">App</span> <span class="o">/></span><span class="p">,</span>
|
|
<span class="nb">document</span><span class="p">.</span><span class="nx">getElementById</span><span class="p">(</span><span class="s1">'root'</span><span class="p">)</span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p><a href="http://codepen.io/gaearon/pen/KgQKPr?editors=0010">Try it on CodePen.</a></p>
|
|
|
|
<p>Typically, new React apps have a single <code>App</code> component at the very top. However, if you integrate React into an existing app, you might start bottom-up with a small component like <code>Button</code> and gradually work your way to the top of the view hierarchy.</p>
|
|
|
|
<blockquote>
|
|
<p><strong>Caveat:</strong></p>
|
|
|
|
<p>Components must return a single root element. This is why we added a <code><div></code> to contain all the <code><Welcome /></code> elements.</p>
|
|
</blockquote>
|
|
|
|
<h2>Extracting Components</h2>
|
|
|
|
<p>Don't be afraid to split components into smaller components.</p>
|
|
|
|
<p>For example, consider this <code>Comment</code> component:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">Comment</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment"</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"UserInfo"</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">img</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Avatar"</span>
|
|
<span class="nx">src</span><span class="o">=</span><span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">author</span><span class="p">.</span><span class="nx">avatarUrl</span><span class="p">}</span>
|
|
<span class="nx">alt</span><span class="o">=</span><span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">author</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span>
|
|
<span class="o">/></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"UserInfo-name"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">author</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment-text"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">text</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment-date"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">formatDate</span><span class="p">(</span><span class="nx">props</span><span class="p">.</span><span class="nx">date</span><span class="p">)}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="p">);</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p><a href="http://codepen.io/gaearon/pen/VKQwEo?editors=0010">Try it on CodePen.</a></p>
|
|
|
|
<p>It accepts <code>author</code> (an object), <code>text</code> (a string), and <code>date</code> (a date) as props, and describes a comment on a social media website.</p>
|
|
|
|
<p>This component can be tricky to change because of all the nesting, and it is also hard to reuse individual parts of it. Let's extract a few components from it.</p>
|
|
|
|
<p>First, we will extract <code>Avatar</code>:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">Avatar</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="hll"> <span class="o"><</span><span class="nx">img</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Avatar"</span>
|
|
</span><span class="hll"> <span class="nx">src</span><span class="o">=</span><span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">user</span><span class="p">.</span><span class="nx">avatarUrl</span><span class="p">}</span>
|
|
</span><span class="hll"> <span class="nx">alt</span><span class="o">=</span><span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">user</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span>
|
|
</span><span class="hll"> <span class="o">/></span>
|
|
</span> <span class="p">);</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p>The <code>Avatar</code> doesn't need to know that it is being rendered inside a <code>Comment</code>. This is why we have given its prop a more generic name: <code>user</code> rather than <code>author</code>.</p>
|
|
|
|
<p>We recommend naming props from the component's own point of view rather than the context in which it is being used.</p>
|
|
|
|
<p>We can now simplify <code>Comment</code> a tiny bit:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">Comment</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment"</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"UserInfo"</span><span class="o">></span>
|
|
<span class="hll"> <span class="o"><</span><span class="nx">Avatar</span> <span class="nx">user</span><span class="o">=</span><span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">author</span><span class="p">}</span> <span class="o">/></span>
|
|
</span> <span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"UserInfo-name"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">author</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment-text"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">text</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment-date"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">formatDate</span><span class="p">(</span><span class="nx">props</span><span class="p">.</span><span class="nx">date</span><span class="p">)}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="p">);</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p>Next, we will extract a <code>UserInfo</code> component that renders an <code>Avatar</code> next to user's name:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">UserInfo</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="hll"> <span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"UserInfo"</span><span class="o">></span>
|
|
</span><span class="hll"> <span class="o"><</span><span class="nx">Avatar</span> <span class="nx">user</span><span class="o">=</span><span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">user</span><span class="p">}</span> <span class="o">/></span>
|
|
</span><span class="hll"> <span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"UserInfo-name"</span><span class="o">></span>
|
|
</span><span class="hll"> <span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">user</span><span class="p">.</span><span class="nx">name</span><span class="p">}</span>
|
|
</span><span class="hll"> <span class="o"><</span><span class="err">/div></span>
|
|
</span><span class="hll"> <span class="o"><</span><span class="err">/div></span>
|
|
</span> <span class="p">);</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p>This lets us simplify <code>Comment</code> even further:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">Comment</span><span class="p">(</span><span class="nx">props</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment"</span><span class="o">></span>
|
|
<span class="hll"> <span class="o"><</span><span class="nx">UserInfo</span> <span class="nx">user</span><span class="o">=</span><span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">author</span><span class="p">}</span> <span class="o">/></span>
|
|
</span> <span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment-text"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">text</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="s2">"Comment-date"</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">formatDate</span><span class="p">(</span><span class="nx">props</span><span class="p">.</span><span class="nx">date</span><span class="p">)}</span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="o"><</span><span class="err">/div></span>
|
|
<span class="p">);</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p><a href="http://codepen.io/gaearon/pen/rrJNJY?editors=0010">Try it on CodePen.</a></p>
|
|
|
|
<p>Extracting components might seem like grunt work at first, but having a palette of reusable components pays off in larger apps. A good rule of thumb is that if a part of your UI is used several times (<code>Button</code>, <code>Panel</code>, <code>Avatar</code>), or is complex enough on its own (<code>App</code>, <code>FeedStory</code>, <code>Comment</code>), it is a good candidate to be a reusable component.</p>
|
|
|
|
<h2>Props are Read-Only</h2>
|
|
|
|
<p>Whether you declare a component <a href="#functional-and-class-components">as a function or a class</a>, it must never modify its own props. Consider this <code>sum</code> function:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">sum</span><span class="p">(</span><span class="nx">a</span><span class="p">,</span> <span class="nx">b</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="nx">a</span> <span class="o">+</span> <span class="nx">b</span><span class="p">;</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p>Such functions are called <a href="https://en.wikipedia.org/wiki/Pure_function">"pure"</a> because they do not attempt to change their inputs, and always return the same result for the same inputs.</p>
|
|
|
|
<p>In contrast, this function is impure because it changes its own input:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">function</span> <span class="nx">withdraw</span><span class="p">(</span><span class="nx">account</span><span class="p">,</span> <span class="nx">amount</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="nx">account</span><span class="p">.</span><span class="nx">total</span> <span class="o">-=</span> <span class="nx">amount</span><span class="p">;</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div>
|
|
<p>React is pretty flexible but it has a single strict rule:</p>
|
|
|
|
<p><strong>All React components must act like pure functions with respect to their props.</strong></p>
|
|
|
|
<p>Of course, application UIs are dynamic and change over time. In the <a href="/react/docs/state-and-lifecycle.html">next section</a>, we will introduce a new concept of "state". State allows React components to change their output over time in response to user actions, network responses, and anything else, without violating this rule.</p>
|
|
|
|
|
|
<div class="docs-prevnext">
|
|
|
|
<a class="docs-prev" href="/react/docs/rendering-elements.html">← Prev</a>
|
|
|
|
|
|
<a class="docs-next" href="/react/docs/state-and-lifecycle.html">Next →</a>
|
|
|
|
</div>
|
|
</div>
|
|
|
|
<div class="nav-docs">
|
|
<!-- Docs Nav -->
|
|
|
|
<div class="nav-docs-section">
|
|
<h3>Quick Start</h3>
|
|
<ul>
|
|
|
|
<li>
|
|
<a href="/react/docs/installation.html">Installation</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/hello-world.html">Hello World</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/introducing-jsx.html">Introducing JSX</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/rendering-elements.html">Rendering Elements</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/components-and-props.html" class="active">Components and Props</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/state-and-lifecycle.html">State and Lifecycle</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/handling-events.html">Handling Events</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/conditional-rendering.html">Conditional Rendering</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/lists-and-keys.html">Lists and Keys</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/forms.html">Forms</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/lifting-state-up.html">Lifting State Up</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/composition-vs-inheritance.html">Composition vs Inheritance</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/thinking-in-react.html">Thinking In React</a>
|
|
|
|
</li>
|
|
|
|
</ul>
|
|
</div>
|
|
|
|
<div class="nav-docs-section">
|
|
<h3>Advanced Guides</h3>
|
|
<ul>
|
|
|
|
<li>
|
|
<a href="/react/docs/jsx-in-depth.html">JSX In Depth</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/typechecking-with-proptypes.html">Typechecking With PropTypes</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/refs-and-the-dom.html">Refs and the DOM</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/uncontrolled-components.html">Uncontrolled Components</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/optimizing-performance.html">Optimizing Performance</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/react-without-es6.html">React Without ES6</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/react-without-jsx.html">React Without JSX</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/reconciliation.html">Reconciliation</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/context.html">Context</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/portals.html">Portals</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/web-components.html">Web Components</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/higher-order-components.html">Higher-Order Components</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/integrating-with-other-libraries.html">Integrating with Other Libraries</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/accessibility.html">Accessibility</a>
|
|
|
|
</li>
|
|
|
|
</ul>
|
|
</div>
|
|
|
|
<div class="nav-docs-section">
|
|
<h3>Reference</h3>
|
|
<ul>
|
|
|
|
<li>
|
|
<a href="/react/docs/react-api.html">React</a>
|
|
|
|
<ul>
|
|
|
|
<li>
|
|
<a href="/react/docs/react-component.html">React.Component</a>
|
|
</li>
|
|
|
|
</ul>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/react-dom.html">ReactDOM</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/react-dom-server.html">ReactDOMServer</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/dom-elements.html">DOM Elements</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/events.html">SyntheticEvent</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/test-utils.html">Test Utilities</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/shallow-renderer.html">Shallow Renderer</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/test-renderer.html">Test Renderer</a>
|
|
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/docs/javascript-environment-requirements.html">JS Environment Requirements</a>
|
|
|
|
</li>
|
|
|
|
</ul>
|
|
</div>
|
|
|
|
|
|
<!-- Contributing Nav -->
|
|
|
|
<div class="nav-docs-section">
|
|
<h3>Contributing</h3>
|
|
<ul>
|
|
|
|
<li>
|
|
<a href="/react/contributing/how-to-contribute.html">How to Contribute</a>
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/contributing/codebase-overview.html">Codebase Overview</a>
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/contributing/implementation-notes.html">Implementation Notes</a>
|
|
</li>
|
|
|
|
<li>
|
|
<a href="/react/contributing/design-principles.html">Design Principles</a>
|
|
</li>
|
|
|
|
</ul>
|
|
</div>
|
|
|
|
|
|
</div>
|
|
|
|
</section>
|
|
|
|
|
|
<footer class="nav-footer">
|
|
<section class="sitemap">
|
|
<a href="/react/" class="nav-home">
|
|
</a>
|
|
<div>
|
|
<h5><a href="/react/docs/">Docs</a></h5>
|
|
<a href="/react/docs/hello-world.html">Quick Start</a>
|
|
<a href="/react/docs/thinking-in-react.html">Thinking in React</a>
|
|
<a href="/react/tutorial/tutorial.html">Tutorial</a>
|
|
<a href="/react/docs/jsx-in-depth.html">Advanced Guides</a>
|
|
</div>
|
|
<div>
|
|
<h5><a href="/react/community/support.html">Community</a></h5>
|
|
<a href="http://stackoverflow.com/questions/tagged/reactjs" target="_blank">Stack Overflow</a>
|
|
<a href="https://discuss.reactjs.org/" target="_blank">Discussion Forum</a>
|
|
<a href="https://discord.gg/0ZcbPKXt5bZjGY5n" target="_blank">Reactiflux Chat</a>
|
|
<a href="https://www.facebook.com/react" target="_blank">Facebook</a>
|
|
<a href="https://twitter.com/reactjs" target="_blank">Twitter</a>
|
|
</div>
|
|
<div>
|
|
<h5><a href="/react/community/support.html">Resources</a></h5>
|
|
<a href="/react/community/conferences.html">Conferences</a>
|
|
<a href="/react/community/videos.html">Videos</a>
|
|
<a href="https://github.com/facebook/react/wiki/Examples" target="_blank">Examples</a>
|
|
<a href="https://github.com/facebook/react/wiki/Complementary-Tools" target="_blank">Complementary Tools</a>
|
|
</div>
|
|
<div>
|
|
<h5>More</h5>
|
|
<a href="/react/blog/">Blog</a>
|
|
<a href="https://github.com/facebook/react" target="_blank">GitHub</a>
|
|
<a href="http://facebook.github.io/react-native/" target="_blank">React Native</a>
|
|
<a href="/react/acknowledgements.html">Acknowledgements</a>
|
|
</div>
|
|
</section>
|
|
<a href="https://code.facebook.com/projects/" target="_blank" class="fbOpenSource">
|
|
<img src="/react/img/oss_logo.png" alt="Facebook Open Source" width="170" height="45"/>
|
|
</a>
|
|
<section class="copyright">
|
|
Copyright © 2017 Facebook Inc.
|
|
</section>
|
|
</footer>
|
|
|
|
</div>
|
|
|
|
<div id="fb-root"></div>
|
|
<script src="/react/js/anchor-links.js"></script>
|
|
<script>
|
|
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
|
|
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
|
|
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
|
|
})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
|
|
ga('create', 'UA-41298772-1', 'facebook.github.io');
|
|
ga('send', 'pageview');
|
|
|
|
!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="https://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs");
|
|
|
|
(function(d, s, id) {
|
|
var js, fjs = d.getElementsByTagName(s)[0];
|
|
if (d.getElementById(id)) return;
|
|
js = d.createElement(s); js.id = id;
|
|
js.src = "//connect.facebook.net/en_US/sdk.js#xfbml=1&version=v2.6&appId=623268441017527";
|
|
fjs.parentNode.insertBefore(js, fjs);
|
|
}(document, 'script', 'facebook-jssdk'));
|
|
|
|
docsearch({
|
|
apiKey: '36221914cce388c46d0420343e0bb32e',
|
|
indexName: 'react',
|
|
inputSelector: '#algolia-doc-search'
|
|
});
|
|
</script>
|
|
</body>
|
|
</html>
|