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628 lines
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HTML
628 lines
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<a href="/react/tips/props-in-getInitialState-as-anti-pattern.html">Props in getInitialState Is an Anti-Pattern</a>
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<a href="/react/tips/dom-event-listeners.html">DOM Event Listeners in a Component</a>
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<a href="/react/tips/initial-ajax.html">Load Initial Data via AJAX</a>
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<a href="/react/tips/false-in-jsx.html">False in JSX</a>
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<a href="/react/tips/communicate-between-components.html">Communicate Between Components</a>
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<a href="/react/tips/expose-component-functions.html">Expose Component Functions</a>
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<a href="/react/tips/references-to-components.html">References to Components</a>
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<a href="/react/tips/children-undefined.html">this.props.children undefined</a>
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</ul>
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</div>
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</div>
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<div class="inner-content">
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<h1>
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JSX in Depth
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/02.1-jsx-in-depth.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>JSX is a JavaScript XML syntax transform recommended for use
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with React.</p>
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<blockquote>
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<p>Note:</p>
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<p>Don't forget the <code>/** @jsx React.DOM */</code> pragma at the beginning of your file! This tells JSX to process the file for React.</p>
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<p>If you don't include the pragma, your source will remain untouched, so it's safe to run the JSX transformer on all JS files in your codebase if you want to.</p>
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</blockquote>
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<h2><a class="anchor" name="why-jsx"></a>Why JSX? <a class="hash-link" href="#why-jsx">#</a></h2>
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<p>React works out of the box without JSX. Simply construct your markup using the
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functions on <code>React.DOM</code>. For example, here's how to construct a simple link:</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">link</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">DOM</span><span class="p">.</span><span class="nx">a</span><span class="p">({</span><span class="nx">href</span><span class="o">:</span> <span class="s1">'http://facebook.github.io/react'</span><span class="p">},</span> <span class="s1">'React'</span><span class="p">);</span>
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</code></pre></div>
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<p>We recommend using JSX for many reasons:</p>
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<ul>
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<li>It's easier to visualize the structure of the DOM.</li>
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<li>Designers are more comfortable making changes.</li>
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<li>It's familiar for those who have used MXML or XAML.</li>
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</ul>
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<h2><a class="anchor" name="the-transform"></a>The Transform <a class="hash-link" href="#the-transform">#</a></h2>
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<p>JSX transforms from an XML-like syntax into native JavaScript. XML elements and
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attributes are transformed into function calls and objects, respectively.</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Nav</span><span class="p">;</span>
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<span class="c1">// Input (JSX):</span>
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<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Nav</span> <span class="nx">color</span><span class="o">=</span><span class="s2">"blue"</span> <span class="o">/></span><span class="p">;</span>
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<span class="c1">// Output (JS):</span>
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<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="nx">Nav</span><span class="p">({</span><span class="nx">color</span><span class="o">:</span><span class="s2">"blue"</span><span class="p">});</span>
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</code></pre></div>
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<p>Notice that in order to use <code><Nav /></code>, the <code>Nav</code> variable must be in scope.</p>
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<p>JSX also allows specifying children using XML syntax:</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Nav</span><span class="p">,</span> <span class="nx">Profile</span><span class="p">;</span>
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<span class="c1">// Input (JSX):</span>
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<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Nav</span> <span class="nx">color</span><span class="o">=</span><span class="s2">"blue"</span><span class="o">><</span><span class="nx">Profile</span><span class="o">></span><span class="nx">click</span><span class="o"><</span><span class="err">/Profile></Nav>;</span>
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<span class="c1">// Output (JS):</span>
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<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="nx">Nav</span><span class="p">({</span><span class="nx">color</span><span class="o">:</span><span class="s2">"blue"</span><span class="p">},</span> <span class="nx">Profile</span><span class="p">(</span><span class="kc">null</span><span class="p">,</span> <span class="s2">"click"</span><span class="p">));</span>
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</code></pre></div>
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<p>Use the <a href="/react/jsx-compiler.html">JSX Compiler</a> to try out JSX and see how it
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desugars into native JavaScript, and the
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<a href="/react/html-jsx.html">HTML to JSX converter</a> to convert your existing HTML to
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JSX.</p>
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<p>If you want to use JSX, the <a href="/react/docs/getting-started.html">Getting Started</a> guide shows
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how to setup compilation.</p>
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<blockquote>
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<p>Note:</p>
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<p>Details about the code transform are given here to increase understanding, but
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your code should not rely on these implementation details.</p>
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</blockquote>
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<h2><a class="anchor" name="react-and-jsx"></a>React and JSX <a class="hash-link" href="#react-and-jsx">#</a></h2>
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<p>React and JSX are independent technologies, but JSX was primarily built with
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React in mind. The two valid uses of JSX are:</p>
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<ul>
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<li>To construct instances of React DOM components (<code>React.DOM.*</code>).</li>
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<li>To construct instances of composite components created with
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<code>React.createClass()</code>.</li>
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</ul>
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<h3><a class="anchor" name="react-dom-components"></a>React DOM Components <a class="hash-link" href="#react-dom-components">#</a></h3>
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<p>To construct a <code><div></code> is to create a variable that refers to <code>React.DOM.div</code>.</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">div</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">DOM</span><span class="p">.</span><span class="nx">div</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">app</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">"appClass"</span><span class="o">></span><span class="nx">Hello</span><span class="p">,</span> <span class="nx">React</span><span class="o">!<</span><span class="err">/div>;</span>
|
|
</code></pre></div><h3><a class="anchor" name="react-composite-components"></a>React Composite Components <a class="hash-link" href="#react-composite-components">#</a></h3>
|
|
<p>To construct an instance of a composite component, create a variable that
|
|
references the class.</p>
|
|
<div class="highlight"><pre><code class="javascript 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="cm">/*...*/</span><span class="p">});</span>
|
|
<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="o"><</span><span class="nx">MyComponent</span> <span class="nx">someProperty</span><span class="o">=</span><span class="p">{</span><span class="kc">true</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
</code></pre></div>
|
|
<p>JSX will infer the component's name from the variable assignment and specify
|
|
the class's <a href="/react/docs/component-specs.html#displayName">displayName</a> accordingly.</p>
|
|
|
|
<p>See <a href="/react/docs/multiple-components.html">Multiple Components</a> to learn more about using composite components.</p>
|
|
|
|
<blockquote>
|
|
<p>Note:</p>
|
|
|
|
<p>Since JSX is JavaScript, identifiers such as <code>class</code> and <code>for</code> are discouraged
|
|
as XML attribute names. Instead, React DOM components expect attributes like
|
|
<code>className</code> and <code>htmlFor</code>, respectively.</p>
|
|
</blockquote>
|
|
<h2><a class="anchor" name="dom-convenience"></a>DOM Convenience <a class="hash-link" href="#dom-convenience">#</a></h2>
|
|
<p>Having to define variables for every type of DOM element can get tedious
|
|
(e.g. <code>var div, span, h1, h2, ...</code>). JSX provides a convenience to address this
|
|
problem by allowing you to specify a variable in an <code>@jsx</code> docblock field. JSX
|
|
will use that field to find DOM components.</p>
|
|
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="cm">/**</span>
|
|
<span class="cm"> * @jsx React.DOM</span>
|
|
<span class="cm"> */</span>
|
|
<span class="kd">var</span> <span class="nx">Nav</span><span class="p">;</span>
|
|
<span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">tree</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Nav</span><span class="o">><</span><span class="nx">span</span> <span class="o">/><</span><span class="err">/Nav>;</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">tree</span> <span class="o">=</span> <span class="nx">Nav</span><span class="p">(</span><span class="kc">null</span><span class="p">,</span> <span class="nx">React</span><span class="p">.</span><span class="nx">DOM</span><span class="p">.</span><span class="nx">span</span><span class="p">(</span><span class="kc">null</span><span class="p">));</span>
|
|
</code></pre></div>
|
|
<blockquote>
|
|
<p>Remember:</p>
|
|
|
|
<p>JSX simply transforms elements into function calls and has no notion of the
|
|
DOM. The docblock parameter is only a convenience to resolve the most commonly
|
|
used elements. In general, JSX has no notion of the DOM.</p>
|
|
</blockquote>
|
|
<h2><a class="anchor" name="javascript-expressions"></a>JavaScript Expressions <a class="hash-link" href="#javascript-expressions">#</a></h2><h3><a class="anchor" name="attribute-expressions"></a>Attribute Expressions <a class="hash-link" href="#attribute-expressions">#</a></h3>
|
|
<p>To use a JavaScript expression as an attribute value, wrap the expression in a
|
|
pair of curly braces (<code>{}</code>) instead of quotes (<code>""</code>).</p>
|
|
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">person</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Person</span> <span class="nx">name</span><span class="o">=</span><span class="p">{</span><span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nb">window</span><span class="p">.</span><span class="nx">name</span> <span class="o">:</span> <span class="s1">''</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">person</span> <span class="o">=</span> <span class="nx">Person</span><span class="p">({</span><span class="nx">name</span><span class="o">:</span> <span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nb">window</span><span class="p">.</span><span class="nx">name</span> <span class="o">:</span> <span class="s1">''</span><span class="p">});</span>
|
|
</code></pre></div><h3><a class="anchor" name="child-expressions"></a>Child Expressions <a class="hash-link" href="#child-expressions">#</a></h3>
|
|
<p>Likewise, JavaScript expressions may be used to express children:</p>
|
|
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">content</span> <span class="o">=</span> <span class="o"><</span><span class="nx">Container</span><span class="o">></span><span class="p">{</span><span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="o"><</span><span class="nx">Nav</span> <span class="o">/></span> <span class="o">:</span> <span class="o"><</span><span class="nx">Login</span> <span class="o">/></span><span class="p">}</span><span class="o"><</span><span class="err">/Container>;</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">content</span> <span class="o">=</span> <span class="nx">Container</span><span class="p">(</span><span class="kc">null</span><span class="p">,</span> <span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nx">Nav</span><span class="p">(</span><span class="kc">null</span><span class="p">)</span> <span class="o">:</span> <span class="nx">Login</span><span class="p">(</span><span class="kc">null</span><span class="p">));</span>
|
|
</code></pre></div><h3><a class="anchor" name="comments"></a>Comments <a class="hash-link" href="#comments">#</a></h3>
|
|
<p>It's easy to add comments within your JSX; they're just JS expressions. You just need to be careful to put <code>{}</code> around the comments when you are within the children section of a tag.</p>
|
|
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">content</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">Nav</span><span class="o">></span>
|
|
<span class="p">{</span><span class="cm">/* child comment, put {} around */</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="nx">Person</span>
|
|
<span class="cm">/* multi</span>
|
|
<span class="cm"> line</span>
|
|
<span class="cm"> comment */</span>
|
|
<span class="nx">name</span><span class="o">=</span><span class="p">{</span><span class="nb">window</span><span class="p">.</span><span class="nx">isLoggedIn</span> <span class="o">?</span> <span class="nb">window</span><span class="p">.</span><span class="nx">name</span> <span class="o">:</span> <span class="s1">''</span><span class="p">}</span> <span class="c1">// end of line comment</span>
|
|
<span class="o">/></span>
|
|
<span class="o"><</span><span class="err">/Nav></span>
|
|
<span class="p">);</span>
|
|
</code></pre></div><h2><a class="anchor" name="prior-work"></a>Prior Work <a class="hash-link" href="#prior-work">#</a></h2>
|
|
<p>JSX is similar to several other JavaScript embedded XML language
|
|
proposals/projects. Some of the features of JSX that distinguish it from similar
|
|
efforts include:</p>
|
|
|
|
<ul>
|
|
<li>JSX is a simple syntactic transform.</li>
|
|
<li>JSX neither provides nor requires a runtime library.</li>
|
|
<li>JSX does not alter or add to the semantics of JavaScript.</li>
|
|
</ul>
|
|
|
|
<p>JSX is similar to HTML, but not exactly the same. See <a href="/react/docs/jsx-gotchas.html">JSX gotchas</a> for some key differences.</p>
|
|
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