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Dan Abramov
553 lines
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HTML
553 lines
22 KiB
HTML
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<a href="/react/tips/children-undefined.html">this.props.children undefined</a>
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<a href="/react/tips/use-react-with-other-libraries.html">Use React with Other Libraries</a>
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<a href="/react/contributing/how-to-contribute.html">How to Contribute</a>
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<li>
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<a href="/react/contributing/design-principles.html">Design Principles</a>
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</div>
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</div>
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<div class="inner-content">
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/ref-02-component-api.md" target="_blank">Edit on GitHub</a>
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<h1>
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Component API
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</h1>
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<div class="subHeader"></div>
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<h2><a class="anchor" name="react.component"></a>React.Component <a class="hash-link" href="#react.component">#</a></h2>
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<p>Instances of a React Component are created internally in React when rendering. These instances are reused in subsequent renders, and can be accessed in your component methods as <code>this</code>. The only way to get a handle to a React Component instance outside of React is by storing the return value of <code>ReactDOM.render</code>. Inside other Components, you may use <a href="/react/docs/more-about-refs.html">refs</a> to achieve the same result.</p>
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<h3><a class="anchor" name="setstate"></a>setState <a class="hash-link" href="#setstate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">setState</span><span class="p">(</span>
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<span class="kd">function</span><span class="o">|</span><span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span>
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<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
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<span class="p">)</span>
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</code></pre></div>
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<p>Performs a shallow merge of nextState into current state. This is the primary method you use to trigger UI updates from event handlers and server request callbacks.</p>
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<p>The first argument can be an object (containing zero or more keys to update) or a function (of state and props) that returns an object containing keys to update.</p>
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<p>Here is the simple object usage:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">setState</span><span class="p">({</span><span class="nx">mykey</span><span class="o">:</span> <span class="s1">'my new value'</span><span class="p">});</span>
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</code></pre></div>
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<p>It's also possible to pass a function with the signature <code>function(state, props)</code>. This can be useful in some cases when you want to enqueue an atomic update that consults the previous value of state+props before setting any values. For instance, suppose we wanted to increment a value in state:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">setState</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">previousState</span><span class="p">,</span> <span class="nx">currentProps</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">return</span> <span class="p">{</span><span class="nx">myInteger</span><span class="o">:</span> <span class="nx">previousState</span><span class="p">.</span><span class="nx">myInteger</span> <span class="o">+</span> <span class="mi">1</span><span class="p">};</span>
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<span class="p">});</span>
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</code></pre></div>
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<p>The second (optional) parameter is a callback function that will be executed once <code>setState</code> is completed and the component is re-rendered.</p>
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<blockquote>
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<p>Notes:</p>
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<p><em>NEVER</em> mutate <code>this.state</code> directly, as calling <code>setState()</code> afterwards may replace the mutation you made. Treat <code>this.state</code> as if it were immutable.</p>
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<p><code>setState()</code> does not immediately mutate <code>this.state</code> but creates a pending state transition. Accessing <code>this.state</code> after calling this method can potentially return the existing value.</p>
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<p>There is no guarantee of synchronous operation of calls to <code>setState</code> and calls may be batched for performance gains.</p>
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<p><code>setState()</code> will always trigger a re-render unless conditional rendering logic is implemented in <code>shouldComponentUpdate()</code>. If mutable objects are being used and the logic cannot be implemented in <code>shouldComponentUpdate()</code>, calling <code>setState()</code> only when the new state differs from the previous state will avoid unnecessary re-renders.</p>
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</blockquote>
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<h3><a class="anchor" name="replacestate"></a>replaceState <a class="hash-link" href="#replacestate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">replaceState</span><span class="p">(</span>
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<span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span>
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<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
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<span class="p">)</span>
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</code></pre></div>
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<p>Like <code>setState()</code> but deletes any pre-existing state keys that are not in nextState.</p>
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<blockquote>
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<p>Note:</p>
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<p>This method is not available on ES6 <code>class</code> components that extend <code>React.Component</code>. It may be removed entirely in a future version of React.</p>
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</blockquote>
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<h3><a class="anchor" name="forceupdate"></a>forceUpdate <a class="hash-link" href="#forceupdate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">forceUpdate</span><span class="p">(</span>
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<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
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<span class="p">)</span>
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</code></pre></div>
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<p>By default, when your component's state or props change, your component will re-render. However, if these change implicitly (eg: data deep within an object changes without changing the object itself) or if your <code>render()</code> method depends on some other data, you can tell React that it needs to re-run <code>render()</code> by calling <code>forceUpdate()</code>.</p>
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<p>Calling <code>forceUpdate()</code> will cause <code>render()</code> to be called on the component, skipping <code>shouldComponentUpdate()</code>. This will trigger the normal lifecycle methods for child components, including the <code>shouldComponentUpdate()</code> method of each child. React will still only update the DOM if the markup changes.</p>
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<p>Normally you should try to avoid all uses of <code>forceUpdate()</code> and only read from <code>this.props</code> and <code>this.state</code> in <code>render()</code>. This makes your component "pure" and your application much simpler and more efficient.</p>
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<h3><a class="anchor" name="ismounted"></a>isMounted <a class="hash-link" href="#ismounted">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kr">boolean</span> <span class="nx">isMounted</span><span class="p">()</span>
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</code></pre></div>
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<p><code>isMounted()</code> returns <code>true</code> if the component is rendered into the DOM, <code>false</code> otherwise. You can use this method to guard asynchronous calls to <code>setState()</code> or <code>forceUpdate()</code>.</p>
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<blockquote>
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<p>Note:</p>
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<p>This method is not available on ES6 <code>class</code> components that extend <code>React.Component</code>. It will likely be removed entirely in a future version of React, so you might as well <a href="/react/blog/2015/12/16/ismounted-antipattern.html">start migrating away from isMounted() now</a>.</p>
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</blockquote>
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