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Cheng Lou	chenglou	docs fix back link in Examples	6b15ad5
Cheng Lou	chenglou	docs add jsx->js tab to live editors	7ac5f3c
Paul O’Shannessy	zpao	Normalize line endings	6b1c6be
Ben Alpert	spicyj	Update homepage for new JSX/JS editor	761e1c8
Ben Alpert	spicyj	Properly clear live editor on JSX compile failure	d3fc5ad
Ben Alpert	spicyj	Simplify live editor execution logic	c7f0663
Cheng Lou	chenglou	[docs] Tweak frontpage first example and jsx-compiler example	8c8841c
Christoph Pojer	cpojer	Update propTypes documentation.	b66fbde
Jean Lauliac	jeanlauliac	Update broken link in 'why react' article	341d292
Jean Lauliac	jeanlauliac	Normalize internal links in 'why react' article	0681d13
aymanosman	aymanosman	Fix typo	09650e1
Bob Eagan	bobeagan	fix incorrect link	2edb76f
Bob Eagan	bobeagan	add hash link for lifecycle section of working with the browser page	3db3460
Pete Hunt	petehunt	remove references to react-page	3120192
Ben Alpert	spicyj	Fix docs typo	6e4ddfd
Paul O’Shannessy	zpao	Fix animation example code …	dd66223
Eric Schoffstall	Contra	fix grammar mistake	64ac427
Kunal Mehta	kmeht	Add documentation about React.renderComponent …	f970453
Christopher Chedeau	vjeux	s/Mock DOM/Virtual DOM/ …	22772c9
Ben Alpert	spicyj	Disable CodeMirror smart indentation …	571d173
Ben Alpert	spicyj	[docs] Fix comma splice	3810c83
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<h1>Reusable Components</h1>
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<p>When designing interfaces, break down the common design elements (buttons, form fields, layout components, etc) into reusable components with well-defined interfaces. That way, the next time you need to build some UI you can write much less code, which means faster development time, less bugs, and less bytes down the wire.</p>
<h2><a class="anchor" name="prop-validation"></a>Prop Validation <a class="hash-link" href="#prop-validation">#</a></h2>
<p>As your app grows it&#39;s helpful to ensure that your components are used correctly. We do this by allowing you to specify <code>propTypes</code>. <code>React.PropTypes</code> exports a range of validators that can be used to make sure the data you receive is valid. When an invalid value is provided for a prop, a warning will be shown in the JavaScript console. Note that for performance reasons <code>propTypes</code> is only checked in development mode. Here is an example documenting the different validators provided:</p>
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
<span class="nx">propTypes</span><span class="o">:</span> <span class="p">{</span>
<span class="c1">// You can declare that a prop is a specific JS primitive. By default, these</span>
<span class="c1">// are all optional.</span>
<span class="nx">optionalArray</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">array</span><span class="p">,</span>
<span class="nx">optionalBool</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">bool</span><span class="p">,</span>
<span class="nx">optionalFunc</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">func</span><span class="p">,</span>
<span class="nx">optionalNumber</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">number</span><span class="p">,</span>
<span class="nx">optionalObject</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">object</span><span class="p">,</span>
<span class="nx">optionalString</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">string</span><span class="p">,</span>
<span class="c1">// You can ensure that your prop is limited to specific values by treating</span>
<span class="c1">// it as an enum.</span>
<span class="nx">optionalEnum</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">oneOf</span><span class="p">([</span><span class="s1">&#39;News&#39;</span><span class="p">,</span><span class="s1">&#39;Photos&#39;</span><span class="p">]),</span>
<span class="c1">// You can also declare that a prop is an instance of a class. This uses</span>
<span class="c1">// JS&#39;s instanceof operator.</span>
<span class="nx">someClass</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">instanceOf</span><span class="p">(</span><span class="nx">SomeClass</span><span class="p">),</span>
<span class="c1">// You can chain any of the above with isRequired to make sure a warning is</span>
<span class="c1">// shown if the prop isn&#39;t provided.</span>
<span class="nx">requiredFunc</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">func</span><span class="p">.</span><span class="nx">isRequired</span>
<span class="c1">// You can also specify a custom validator.</span>
<span class="nx">customProp</span><span class="o">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">props</span><span class="p">,</span> <span class="nx">propName</span><span class="p">,</span> <span class="nx">componentName</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="sr">/matchme/</span><span class="p">.</span><span class="nx">test</span><span class="p">(</span><span class="nx">props</span><span class="p">[</span><span class="nx">propName</span><span class="p">]))</span> <span class="p">{</span>
<span class="nx">console</span><span class="p">.</span><span class="nx">warn</span><span class="p">(</span><span class="s1">&#39;Validation failed!&#39;</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">},</span>
<span class="cm">/* ... */</span>
<span class="p">});</span>
</code></pre></div><h2><a class="anchor" name="default-prop-values"></a>Default Prop Values <a class="hash-link" href="#default-prop-values">#</a></h2>
<p>React lets you define default values for your <code>props</code> in a very declarative way:</p>
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">ComponentWithDefaultProps</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">getDefaultProps</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">return</span> <span class="p">{</span>
<span class="nx">value</span><span class="o">:</span> <span class="s1">&#39;default value&#39;</span>
<span class="p">};</span>
<span class="p">}</span>
<span class="cm">/* ... */</span>
<span class="p">});</span>
</code></pre></div>
<p>The result of <code>getDefaultProps()</code> will be cached and used to ensure that <code>this.props.value</code> will have a value if it was not specified by the parent component. This allows you to safely just use your props without having to write repetitive and fragile code to handle that yourself.</p>
<h2><a class="anchor" name="transferring-props-a-shortcut"></a>Transferring Props: A Shortcut <a class="hash-link" href="#transferring-props-a-shortcut">#</a></h2>
<p>A common type of React component is one that extends a basic HTML in a simple way. Often you&#39;ll want to copy any HTML attributes passed to your component to the underlying HTML element to save typing. React provides <code>transferPropsTo()</code> to do just this.</p>
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="cm">/** @jsx React.DOM */</span>
<span class="kd">var</span> <span class="nx">CheckLink</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">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="c1">// transferPropsTo() will take any props passed to CheckLink</span>
<span class="c1">// and copy them to &lt;a&gt;</span>
<span class="k">return</span> <span class="k">this</span><span class="p">.</span><span class="nx">transferPropsTo</span><span class="p">(</span><span class="o">&lt;</span><span class="nx">a</span><span class="o">&gt;</span><span class="p">{</span><span class="s1">&#39;&#39;</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">children</span><span class="p">}</span><span class="o">&lt;</span><span class="err">/a&gt;);</span>
<span class="p">}</span>
<span class="p">});</span>
<span class="nx">React</span><span class="p">.</span><span class="nx">renderComponent</span><span class="p">(</span>
<span class="o">&lt;</span><span class="nx">CheckLink</span> <span class="nx">href</span><span class="o">=</span><span class="s2">&quot;javascript:alert(&#39;Hello, world!&#39;);&quot;</span><span class="o">&gt;</span>
<span class="nx">Click</span> <span class="nx">here</span><span class="o">!</span>
<span class="o">&lt;</span><span class="err">/CheckLink&gt;,</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="mixins"></a>Mixins <a class="hash-link" href="#mixins">#</a></h2>
<p>Components are the best way to reuse code in React, but sometimes very different components may share some common functionality. These are sometimes called <a href="http://en.wikipedia.org/wiki/Cross-cutting_concern">cross-cutting concerns</a>. React provides <code>mixins</code> to solve this problem.</p>
<p>One common use case is a component wanting to update itself on a time interval. It&#39;s easy to use <code>setInterval()</code>, but it&#39;s important to cancel your interval when you don&#39;t need it anymore to save memory. React provides <a href="/react/docs/working-with-the-browser.html#component-lifecycle">lifecycle methods</a> that let you know when a component is about to be created or destroyed. Let&#39;s create a simple mixin that uses these methods to provide an easy <code>setInterval()</code> function that will automatically get cleaned up when your component is destroyed.</p>
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="cm">/** @jsx React.DOM */</span>
<span class="kd">var</span> <span class="nx">SetIntervalMixin</span> <span class="o">=</span> <span class="p">{</span>
<span class="nx">componentWillMount</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">this</span><span class="p">.</span><span class="nx">intervals</span> <span class="o">=</span> <span class="p">[];</span>
<span class="p">},</span>
<span class="nx">setInterval</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">this</span><span class="p">.</span><span class="nx">intervals</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="nx">setInterval</span><span class="p">.</span><span class="nx">apply</span><span class="p">(</span><span class="kc">null</span><span class="p">,</span> <span class="nx">arguments</span><span class="p">));</span>
<span class="p">},</span>
<span class="nx">componentWillUnmount</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">this</span><span class="p">.</span><span class="nx">intervals</span><span class="p">.</span><span class="nx">map</span><span class="p">(</span><span class="nx">clearInterval</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">};</span>
<span class="kd">var</span> <span class="nx">TickTock</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">mixins</span><span class="o">:</span> <span class="p">[</span><span class="nx">SetIntervalMixin</span><span class="p">],</span> <span class="c1">// Use the mixin</span>
<span class="nx">getInitialState</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">return</span> <span class="p">{</span><span class="nx">seconds</span><span class="o">:</span> <span class="mi">0</span><span class="p">};</span>
<span class="p">},</span>
<span class="nx">componentDidMount</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">this</span><span class="p">.</span><span class="nx">setInterval</span><span class="p">(</span><span class="k">this</span><span class="p">.</span><span class="nx">tick</span><span class="p">,</span> <span class="mi">1000</span><span class="p">);</span> <span class="c1">// Call a method on the mixin</span>
<span class="p">},</span>
<span class="nx">tick</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">this</span><span class="p">.</span><span class="nx">setState</span><span class="p">({</span><span class="nx">seconds</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">state</span><span class="p">.</span><span class="nx">seconds</span> <span class="o">+</span> <span class="mi">1</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="k">return</span> <span class="p">(</span>
<span class="o">&lt;</span><span class="nx">p</span><span class="o">&gt;</span>
<span class="nx">React</span> <span class="nx">has</span> <span class="nx">been</span> <span class="nx">running</span> <span class="k">for</span> <span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">state</span><span class="p">.</span><span class="nx">seconds</span><span class="p">}</span> <span class="nx">seconds</span><span class="p">.</span>
<span class="o">&lt;</span><span class="err">/p&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">renderComponent</span><span class="p">(</span>
<span class="o">&lt;</span><span class="nx">TickTock</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>
<p>A nice feature of mixins is that if a component is using multiple mixins and several mixins define the same lifecycle method (i.e. several mixins want to do some cleanup when the component is destroyed), all of the lifecycle methods are guaranteed to be called.</p>
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