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415 lines
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HTML
415 lines
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HTML
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Supported Tags and Attributes
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Event System
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DOM Differences
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</div>
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</div>
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<div class="inner-content">
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<h1>JSX in Depth</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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<h2 id="why-jsx" class="anchor"><a href="#why-jsx">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 id="the-transform" class="anchor"><a href="#the-transform">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.</p>
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<p>If you want to use JSX, the <a href="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 id="react-and-jsx" class="anchor"><a href="#react-and-jsx">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 id="react-dom-components" class="anchor"><a href="#react-dom-components">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>
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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><h3 id="react-composite-components" class="anchor"><a href="#react-composite-components">React Composite Components</a></h3>
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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="multiple-components.html">Multiple Components</a> to learn more about using composite 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 id="dom-convenience" class="anchor"><a href="#dom-convenience">DOM Convenience</a></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="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>
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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 id="javascript-expressions" class="anchor"><a href="#javascript-expressions">JavaScript Expressions</a></h2><h3 id="attribute-expressions" class="anchor"><a href="#attribute-expressions">Attribute Expressions</a></h3>
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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><h3 id="child-expressions" class="anchor"><a href="#child-expressions">Child Expressions</a></h3>
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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="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>
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</code></pre></div><h3 id="comments" class="anchor"><a href="#comments">Comments</a></h3>
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<p>It's easy to add comments within your JSX; they're just JS expressions:</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">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="cm">/* this is a comment */</span><span class="p">}</span><span class="o"><</span><span class="nx">Nav</span> <span class="o">/><</span><span class="err">/Container>;</span>
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</code></pre></div><h2 id="tooling" class="anchor"><a href="#tooling">Tooling</a></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).
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<ul>
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<li>JSX syntax highlighting is available for Sublime Text and other editors
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that support <code>*.tmLanguage</code> using the third-party
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<a href="https://github.com/yungsters/sublime/blob/master/tmLanguage/JavaScript%20(JSX).tmLanguage"><code>JavaScript (JSX).tmLanguage</code></a>.</li>
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</ul></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 id="prior-work" class="anchor"><a href="#prior-work">Prior Work</a></h2>
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|
<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>
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|
|
|
<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>
|
|
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|
<p>JSX is similar to HTML, but not exactly the same. See <a href="./jsx-gotchas.html">JSX gotchas</a> for some key differences.</p>
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