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Paul O’Shannessy
236 lines
14 KiB
HTML
236 lines
14 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
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<title>React | JSX Syntax</title>
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<meta property="og:title" content="React | JSX Syntax" />
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<a class="nav-home" href="/react/index.html">
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React
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<ul class="nav-site">
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<li><a href="/react/docs/getting-started.html" class="active">docs</a></li>
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<li><a href="/react/support.html">support</a></li>
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<section class="content wrap documentationContent">
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<div class="nav-docs">
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<div class="nav-docs-section">
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<h3>Getting started</h3>
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<li><a href="/react/docs/getting-started.html">Getting Started</a></li>
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<li><a href="/react/docs/tutorial.html">Tutorial</a></li>
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<li><a href="/react/docs/common-questions.html">Common Questions</a></li>
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</ul>
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</div>
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<div class="nav-docs-section">
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<h3>Reference</h3>
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<ul>
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<li><a href="/react/docs/syntax.html" class="active">JSX Syntax</a></li>
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<li><a href="/react/docs/component-basics.html">Component Basics</a></li>
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<li><a href="/react/docs/component-data.html">Component Data</a></li>
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<li><a href="/react/docs/component-lifecycle.html">Component Lifecycle</a></li>
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<li><a href="/react/docs/event-handling.html">Event Handling</a></li>
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<li><a href="/react/docs/advanced-components.html">Advanced Components</a></li>
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<li><a href="/react/docs/api.html">API</a></li>
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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>JSX Syntax</h1>
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<div class="subHeader">Writing JavaScript with XML syntax.</div>
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<p>JSX is a JavaScript XML syntax extension recommended (but not required) for use
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with React.</p>
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<p>JSX makes code that deeply nested React components more readable, and writing it
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feels like writing HTML. React documentation examples make use of JSX.</p>
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<h2>The Transform</h2>
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<p>JSX transforms XML-like syntax into native JavaScript. It turns XML elements and
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attributes 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="s1">'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="s1">'blue'</span><span class="p">},</span> <span class="nx">Profile</span><span class="p">({},</span> <span class="s1">'click'</span><span class="p">));</span>
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</code></pre></div>
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<p>The <a href="getting-started.html">Getting Started</a> guide shows how to setup JSX
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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>React and JSX</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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<p><strong>React DOM Components</strong></p>
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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>
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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">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>
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</code></pre></div>
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<p><strong>React Component Components</strong></p>
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<p>To construct an instance of a composite component, create a variable that
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references the class.</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">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>
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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">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>
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</code></pre></div>
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<p>See <a href="component-basics.html">Component Basics</a> to learn more about components.</p>
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<blockquote>
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<p>Note:</p>
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<p>Since JSX is JavaScript, identifiers such as <code>class</code> and <code>for</code> are discouraged
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as XML attribute names. Instead, React DOM components expect attributes like
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<code>className</code> and <code>htmlFor</code>, respectively.</p>
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</blockquote>
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<h2>DOM Convenience</h2>
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<p>Having to define variables for every type of DOM element can get tedious
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(e.g. <code>var div, span, h1, h2, ...</code>). JSX provides a convenience to address this
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problem by allowing you to specify a variable in an <code>@jsx</code> docblock field. JSX
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will use that field to find DOM components.</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="cm">/**</span>
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<span class="cm"> * @jsx React.DOM</span>
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<span class="cm"> */</span>
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<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">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>
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<span class="c1">// Output (JS):</span>
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<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="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>
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</code></pre></div>
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<blockquote>
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<p>Remember:</p>
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<p>JSX simply transforms elements into function calls and has no notion of the
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DOM. The docblock parameter is only a convenience to resolve the most commonly
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used elements. In general, JSX has no notion of the DOM.</p>
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</blockquote>
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<h2>JavaScript Expressions</h2>
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<h4>Attribute Expressions</h4>
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<p>To use a JavaScript expression as an attribute value, wrap the expression in a
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pair of curly braces (<code>{}</code>) instead of quotes (<code>""</code>).</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
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<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>
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<span class="c1">// Output (JS):</span>
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<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>
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</code></pre></div>
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<h4>Child Expressions</h4>
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<p>Likewise, JavaScript expressions may be used to express children:</p>
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<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
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<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>
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<span class="c1">// Output (JS):</span>
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<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="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>
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</code></pre></div>
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<h2>Tooling</h2>
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<p>Beyond the compilation step, JSX does not require any special tools.</p>
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<ul>
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<li>Many editors already include reasonable support for JSX (Vim, Emacs js2-mode).</li>
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<li>Linting provides accurate line numbers after compiling without sourcemaps.</li>
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<li>Elements use standard scoping so linters can find usage of out-of-scope
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components.</li>
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</ul>
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<h2>Prior Work</h2>
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<p>JSX is similar to several other JavaScript embedded XML language
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proposals/projects. Some of the features of JSX that distinguish it from similar
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efforts include:</p>
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<ul>
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<li>JSX is a simple syntactic transform.</li>
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<li>JSX neither provides nor requires a runtime library.</li>
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<li>JSX does not alter or add to the semantics of JavaScript.</li>
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</ul>
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<div class="docs-prevnext">
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<div class="left">A Facebook & Instagram collaboration.</div>
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