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JSX Spread Attributes
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/02.2-jsx-spread.md" target="_blank">Edit on GitHub</a>
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</h1>
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<div class="subHeader"></div>
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<p>If you know all the properties that you want to place on a component ahead of time, it is easy to use JSX:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"> <span class="kd">var</span> <span class="nx">component</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Component</span> <span class="nx">foo</span><span class="o">=</span><span class="p">{</span><span class="nx">x</span><span class="p">}</span> <span class="nx">bar</span><span class="o">=</span><span class="p">{</span><span class="nx">y</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
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</code></pre></div><h2><a class="anchor" name="mutating-props-is-bad-mkay"></a>Mutating Props is Bad, mkay <a class="hash-link" href="#mutating-props-is-bad-mkay">#</a></h2>
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<p>If you don't know which properties you want to set, you might be tempted to add them onto the object later:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"> <span class="kd">var</span> <span class="nx">component</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Component</span> <span class="o">/></span><span class="p">;</span>
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<span class="nx">component</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">foo</span> <span class="o">=</span> <span class="nx">x</span><span class="p">;</span> <span class="c1">// bad</span>
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<span class="nx">component</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">bar</span> <span class="o">=</span> <span class="nx">y</span><span class="p">;</span> <span class="c1">// also bad</span>
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</code></pre></div>
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<p>This is an anti-pattern because it means that we can't help you check the right propTypes until way later. This means that your propTypes errors end up with a cryptic stack trace.</p>
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<p>The props should be considered immutable at this point. Mutating the props object somewhere else could cause unexpected consequences so ideally it would be a frozen object at this point.</p>
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<h2><a class="anchor" name="spread-attributes"></a>Spread Attributes <a class="hash-link" href="#spread-attributes">#</a></h2>
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<p>Now you can use a new feature of JSX called spread attributes:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"> <span class="kd">var</span> <span class="nx">props</span> <span class="o">=</span> <span class="p">{};</span>
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<span class="nx">props</span><span class="p">.</span><span class="nx">foo</span> <span class="o">=</span> <span class="nx">x</span><span class="p">;</span>
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<span class="nx">props</span><span class="p">.</span><span class="nx">bar</span> <span class="o">=</span> <span class="nx">y</span><span class="p">;</span>
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<span class="kd">var</span> <span class="nx">component</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Component</span> <span class="p">{...</span><span class="nx">props</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
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</code></pre></div>
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<p>The properties of the object that you pass in are copied onto the component's props.</p>
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<p>You can use this multiple times or combine it with other attributes. The specification order is important. Later attributes override previous ones.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"> <span class="kd">var</span> <span class="nx">props</span> <span class="o">=</span> <span class="p">{</span> <span class="nx">foo</span><span class="o">:</span> <span class="s1">'default'</span> <span class="p">};</span>
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<span class="kd">var</span> <span class="nx">component</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Component</span> <span class="p">{...</span><span class="nx">props</span><span class="p">}</span> <span class="nx">foo</span><span class="o">=</span><span class="p">{</span><span class="s1">'override'</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
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<span class="nx">console</span><span class="p">.</span><span class="nx">log</span><span class="p">(</span><span class="nx">component</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">foo</span><span class="p">);</span> <span class="c1">// 'override'</span>
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</code></pre></div><h2><a class="anchor" name="whats-with-the-weird-...-notation"></a>What's with the weird <code>...</code> notation? <a class="hash-link" href="#whats-with-the-weird-...-notation">#</a></h2>
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<p>The <code>...</code> operator (or spread operator) is already supported for <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator">arrays in ES6</a>. There is also an ES7 proposal for <a href="https://github.com/sebmarkbage/ecmascript-rest-spread">Object Rest and Spread Properties</a>. We're taking advantage of these supported and developing standards in order to provide a cleaner syntax in JSX.</p>
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