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Working With the Browser
<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/08-working-with-the-browser.md" target="_blank">Edit on GitHub</a>
</h1>
<div class="subHeader"></div>
<p>React provides powerful abstractions that free you from touching the DOM directly in most cases, but sometimes you simply need to access the underlying API, perhaps to work with a third-party library or existing code.</p>
<h2><a class="anchor" name="the-virtual-dom"></a>The Virtual DOM <a class="hash-link" href="#the-virtual-dom">#</a></h2>
<p>React is so fast because it never talks to the DOM directly. React maintains a fast in-memory representation of the DOM. <code>render()</code> methods return a <em>description</em> of the DOM, and React can diff this description with the in-memory representation to compute the fastest way to update the browser.</p>
<p>Additionally, React implements a full synthetic event system such that all event objects are guaranteed to conform to the W3C spec despite browser quirks, and everything bubbles consistently and in a performant way cross-browser. You can even use some HTML5 events in IE8!</p>
<p>Most of the time you should stay within React&#39;s &quot;faked browser&quot; world since it&#39;s more performant and easier to reason about. However, sometimes you simply need to access the underlying API, perhaps to work with a third-party library like a jQuery plugin. React provides escape hatches for you to use the underlying DOM API directly.</p>
<h2><a class="anchor" name="refs-and-getdomnode"></a>Refs and getDOMNode() <a class="hash-link" href="#refs-and-getdomnode">#</a></h2>
<p>To interact with the browser, you&#39;ll need a reference to a DOM node. Every mounted React component has a <code>getDOMNode()</code> function which you can call to get a reference to it.</p>
<blockquote>
<p>Note:</p>
<p><code>getDOMNode()</code> only works on mounted components (that is, components that have been placed in the DOM). If you try to call this on a component that has not been mounted yet (like calling <code>getDOMNode()</code> in <code>render()</code> on a component that has yet to be created) an exception will be thrown.</p>
</blockquote>
<p>In order to get a reference to a React component, you can either use <code>this</code> to get the current React component, or you can use refs to refer to a component you own. They work like this:</p>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">MyComponent</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
<span class="nx">handleClick</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="c1">// Explicitly focus the text input using the raw DOM API.</span>
<span class="k">this</span><span class="p">.</span><span class="nx">refs</span><span class="p">.</span><span class="nx">myTextInput</span><span class="p">.</span><span class="nx">getDOMNode</span><span class="p">().</span><span class="nx">focus</span><span class="p">();</span>
<span class="p">},</span>
<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="c1">// The ref attribute adds a reference to the component to</span>
<span class="c1">// this.refs when the component is mounted.</span>
<span class="k">return</span> <span class="p">(</span>
<span class="o">&lt;</span><span class="nx">div</span><span class="o">&gt;</span>
<span class="o">&lt;</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">&quot;text&quot;</span> <span class="nx">ref</span><span class="o">=</span><span class="s2">&quot;myTextInput&quot;</span> <span class="o">/&gt;</span>
<span class="o">&lt;</span><span class="nx">input</span>
<span class="nx">type</span><span class="o">=</span><span class="s2">&quot;button&quot;</span>
<span class="nx">value</span><span class="o">=</span><span class="s2">&quot;Focus the text input&quot;</span>
<span class="nx">onClick</span><span class="o">=</span><span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">handleClick</span><span class="p">}</span>
<span class="o">/&gt;</span>
<span class="o">&lt;</span><span class="err">/div&gt;</span>
<span class="p">);</span>
<span class="p">}</span>
<span class="p">});</span>
<span class="nx">React</span><span class="p">.</span><span class="nx">render</span><span class="p">(</span>
<span class="o">&lt;</span><span class="nx">MyComponent</span> <span class="o">/&gt;</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">&#39;example&#39;</span><span class="p">)</span>
<span class="p">);</span>
</code></pre></div><h2><a class="anchor" name="more-about-refs"></a>More About Refs <a class="hash-link" href="#more-about-refs">#</a></h2>
<p>To learn more about refs, including ways to use them effectively, see our <a href="/react/docs/more-about-refs.html">more about refs</a> documentation.</p>
<h2><a class="anchor" name="component-lifecycle"></a>Component Lifecycle <a class="hash-link" href="#component-lifecycle">#</a></h2>
<p>Components have three main parts of their lifecycle:</p>
<ul>
<li><strong>Mounting:</strong> A component is being inserted into the DOM.</li>
<li><strong>Updating:</strong> A component is being re-rendered to determine if the DOM should be updated.</li>
<li><strong>Unmounting:</strong> A component is being removed from the DOM.</li>
</ul>
<p>React provides lifecycle methods that you can specify to hook into this process. We provide <strong>will</strong> methods, which are called right before something happens, and <strong>did</strong> methods which are called right after something happens.</p>
<h3><a class="anchor" name="mounting"></a>Mounting <a class="hash-link" href="#mounting">#</a></h3>
<ul>
<li><code>getInitialState(): object</code> is invoked before a component is mounted. Stateful components should implement this and return the initial state data.</li>
<li><code>componentWillMount()</code> is invoked immediately before mounting occurs.</li>
<li><code>componentDidMount()</code> is invoked immediately after mounting occurs. Initialization that requires DOM nodes should go here.</li>
</ul>
<h3><a class="anchor" name="updating"></a>Updating <a class="hash-link" href="#updating">#</a></h3>
<ul>
<li><code>componentWillReceiveProps(object nextProps)</code> is invoked when a mounted component receives new props. This method should be used to compare <code>this.props</code> and <code>nextProps</code> to perform state transitions using <code>this.setState()</code>.</li>
<li><code>shouldComponentUpdate(object nextProps, object nextState): boolean</code> is invoked when a component decides whether any changes warrant an update to the DOM. Implement this as an optimization to compare <code>this.props</code> with <code>nextProps</code> and <code>this.state</code> with <code>nextState</code> and return false if React should skip updating.</li>
<li><code>componentWillUpdate(object nextProps, object nextState)</code> is invoked immediately before updating occurs. You cannot call <code>this.setState()</code> here.</li>
<li><code>componentDidUpdate(object prevProps, object prevState)</code> is invoked immediately after updating occurs.</li>
</ul>
<h3><a class="anchor" name="unmounting"></a>Unmounting <a class="hash-link" href="#unmounting">#</a></h3>
<ul>
<li><code>componentWillUnmount()</code> is invoked immediately before a component is unmounted and destroyed. Cleanup should go here.</li>
</ul>
<h3><a class="anchor" name="mounted-methods"></a>Mounted Methods <a class="hash-link" href="#mounted-methods">#</a></h3>
<p><em>Mounted</em> composite components also support the following methods:</p>
<ul>
<li><code>getDOMNode(): DOMElement</code> can be invoked on any mounted component in order to obtain a reference to its rendered DOM node.</li>
<li><code>forceUpdate()</code> can be invoked on any mounted component when you know that some deeper aspect of the component&#39;s state has changed without using <code>this.setState()</code>.</li>
</ul>
<h2><a class="anchor" name="browser-support-and-polyfills"></a>Browser Support and Polyfills <a class="hash-link" href="#browser-support-and-polyfills">#</a></h2>
<p>At Facebook, we support older browsers, including IE8. We&#39;ve had polyfills in place for a long time to allow us to write forward-thinking JS. This means we don&#39;t have a bunch of hacks scattered throughout our codebase and we can still expect our code to &quot;just work&quot;. For example, instead of seeing <code>+new Date()</code>, we can just write <code>Date.now()</code>. Since the open source React is the same as what we use internally, we&#39;ve carried over this philosophy of using forward thinking JS.</p>
<p>In addition to that philosophy, we&#39;ve also taken the stance that we, as authors of a JS library, should not be shipping polyfills as a part of our library. If every library did this, there&#39;s a good chance you&#39;d be sending down the same polyfill multiple times, which could be a sizable chunk of dead code. If your product needs to support older browsers, chances are you&#39;re already using something like <a href="https://github.com/kriskowal/es5-shim">es5-shim</a>.</p>
<h3><a class="anchor" name="polyfills-needed-to-support-older-browsers"></a>Polyfills Needed to Support Older Browsers <a class="hash-link" href="#polyfills-needed-to-support-older-browsers">#</a></h3>
<p><code>es5-shim.js</code> from <a href="https://github.com/kriskowal/es5-shim">kriskowal&#39;s es5-shim</a> provides the following that React needs:</p>
<ul>
<li><code>Array.isArray</code></li>
<li><code>Array.prototype.every</code></li>
<li><code>Array.prototype.forEach</code></li>
<li><code>Array.prototype.indexOf</code></li>
<li><code>Array.prototype.map</code></li>
<li><code>Date.now</code></li>
<li><code>Function.prototype.bind</code></li>
<li><code>Object.keys</code></li>
<li><code>String.prototype.split</code></li>
<li><code>String.prototype.trim</code></li>
</ul>
<p><code>es5-sham.js</code>, also from <a href="https://github.com/kriskowal/es5-shim">kriskowal&#39;s es5-shim</a>, provides the following that React needs:</p>
<ul>
<li><code>Object.create</code></li>
<li><code>Object.freeze</code></li>
</ul>
<p>The unminified build of React needs the following from <a href="https://github.com/paulmillr/console-polyfill">paulmillr&#39;s console-polyfill</a>.</p>
<ul>
<li><code>console.*</code></li>
</ul>
<p>When using HTML5 elements in IE8 including <code>&lt;section&gt;</code>, <code>&lt;article&gt;</code>, <code>&lt;nav&gt;</code>, <code>&lt;header&gt;</code>, and <code>&lt;footer&gt;</code>, it&#39;s also necessary to include <a href="https://github.com/aFarkas/html5shiv">html5shiv</a> or a similar script.</p>
<h3><a class="anchor" name="cross-browser-issues"></a>Cross-browser Issues <a class="hash-link" href="#cross-browser-issues">#</a></h3>
<p>Although React is pretty good at abstracting browser differences, some browsers are limited or present quirky behaviors that we couldn&#39;t find a workaround for.</p>
<h4><a class="anchor" name="onscroll-event-on-ie8"></a>onScroll event on IE8 <a class="hash-link" href="#onscroll-event-on-ie8">#</a></h4>
<p>On IE8 the <code>onScroll</code> event doesn&#39;t bubble and IE8 doesn&#39;t have an API to define handlers to the capturing phase of an event, meaning there is no way for React to listen to these events.
Currently a handler to this event is ignored on IE8.</p>
<p>See the <a href="https://github.com/facebook/react/issues/631">onScroll doesn&#39;t work in IE8</a> GitHub issue for more information.</p>
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