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Paul O’Shannessy
639 lines
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HTML
639 lines
34 KiB
HTML
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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/false-in-jsx.html">False in JSX</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/children-undefined.html">this.props.children undefined</a>
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<a href="/react/tips/use-react-with-other-libraries.html">Use React with Other Libraries</a>
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<a href="/react/tips/dangerously-set-inner-html.html">Dangerously Set innerHTML</a>
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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><a href="https://facebook.github.io/jsx/">JSX</a> is a JavaScript syntax extension that looks similar to XML. You can use a simple JSX syntactic transform with React.</p>
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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>You don't have to use JSX with React. You can just use plain JS. However, we recommend using JSX because it is a concise and familiar syntax for defining tree structures with attributes.</p>
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<p>It's more familiar for casual developers such as designers.</p>
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<p>XML has the benefit of balanced opening and closing tags. This helps make large trees easier to read than function calls or object literals.</p>
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<p>It doesn't alter the semantics of JavaScript.</p>
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<h2><a class="anchor" name="html-tags-vs.-react-components"></a>HTML Tags vs. React Components <a class="hash-link" href="#html-tags-vs.-react-components">#</a></h2>
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<p>React can either render HTML tags (strings) or React components (classes).</p>
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<p>To render an HTML tag, just use lower-case tag names in 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">myDivElement</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">"foo"</span> <span class="o">/></span><span class="p">;</span>
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<span class="nx">ReactDOM</span><span class="p">.</span><span class="nx">render</span><span class="p">(</span><span class="nx">myDivElement</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">'example'</span><span class="p">));</span>
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</code></pre></div>
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<p>To render a React Component, just create a local variable that starts with an upper-case letter:</p>
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<div class="highlight"><pre><code class="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">myElement</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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<span class="nx">ReactDOM</span><span class="p">.</span><span class="nx">render</span><span class="p">(</span><span class="nx">myElement</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">'example'</span><span class="p">));</span>
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</code></pre></div>
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<p>React's JSX uses the upper vs. lower case convention to distinguish between local component classes and HTML tags.</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 DOM property
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names like <code>className</code> and <code>htmlFor</code>, respectively.</p>
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</blockquote>
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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>React JSX transforms from an XML-like syntax into native JavaScript. XML elements, attributes and children are transformed into arguments that are passed to <code>React.createElement</code>.</p>
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<div class="highlight"><pre><code class="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">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Nav</span><span class="p">,</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="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>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">app</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span>
|
|
<span class="nx">Nav</span><span class="p">,</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">React</span><span class="p">.</span><span class="nx">createElement</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>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p>JSX will infer the class's <a href="/react/docs/component-specs.html#displayname">displayName</a> from the variable assignment when the displayName is undefined:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Input (JSX):</span>
|
|
<span class="kd">var</span> <span class="nx">Nav</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="p">});</span>
|
|
<span class="c1">// Output (JS):</span>
|
|
<span class="kd">var</span> <span class="nx">Nav</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">displayName</span><span class="o">:</span> <span class="s2">"Nav"</span><span class="p">,</span> <span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>Use the <a href="https://babeljs.io/repl/">Babel REPL</a> to try out JSX and see how it desugars into native JavaScript, and the <a href="/react/html-jsx.html">HTML to JSX converter</a> to convert your existing HTML to JSX.</p>
|
|
|
|
<p>If you want to use JSX, the <a href="/react/docs/getting-started.html">Getting Started</a> guide shows how to set up compilation.</p>
|
|
|
|
<blockquote>
|
|
<p>Note:</p>
|
|
|
|
<p>The JSX expression always evaluates to a ReactElement. The actual
|
|
implementation details may vary. An optimized mode could inline the
|
|
ReactElement as an object literal to bypass the validation code in
|
|
<code>React.createElement</code>.</p>
|
|
</blockquote>
|
|
<h2><a class="anchor" name="namespaced-components"></a>Namespaced Components <a class="hash-link" href="#namespaced-components">#</a></h2>
|
|
<p>If you are building a component that has many children, like a form, you might end up with something with a lot of variable declarations:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Awkward block of variable declarations</span>
|
|
<span class="kd">var</span> <span class="nx">Form</span> <span class="o">=</span> <span class="nx">MyFormComponent</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">FormRow</span> <span class="o">=</span> <span class="nx">Form</span><span class="p">.</span><span class="nx">Row</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">FormLabel</span> <span class="o">=</span> <span class="nx">Form</span><span class="p">.</span><span class="nx">Label</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">FormInput</span> <span class="o">=</span> <span class="nx">Form</span><span class="p">.</span><span class="nx">Input</span><span class="p">;</span>
|
|
|
|
<span class="kd">var</span> <span class="nx">App</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">FormRow</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">FormLabel</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="nx">FormInput</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="err">/FormRow></span>
|
|
<span class="o"><</span><span class="err">/Form></span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p>To make it simpler and easier, <em>namespaced components</em> let you use one component that has other components as attributes:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Form</span> <span class="o">=</span> <span class="nx">MyFormComponent</span><span class="p">;</span>
|
|
|
|
<span class="kd">var</span> <span class="nx">App</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Row</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Label</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Input</span> <span class="o">/></span>
|
|
<span class="o"><</span><span class="err">/Form.Row></span>
|
|
<span class="o"><</span><span class="err">/Form></span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<p>To do this, you just need to create your <em>"sub-components"</em> as attributes of the main component:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">MyFormComponent</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="p">...</span> <span class="p">});</span>
|
|
|
|
<span class="nx">MyFormComponent</span><span class="p">.</span><span class="nx">Row</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="p">...</span> <span class="p">});</span>
|
|
<span class="nx">MyFormComponent</span><span class="p">.</span><span class="nx">Label</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="p">...</span> <span class="p">});</span>
|
|
<span class="nx">MyFormComponent</span><span class="p">.</span><span class="nx">Input</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="p">...</span> <span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>JSX will handle this properly when compiling your code.</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">App</span> <span class="o">=</span> <span class="p">(</span>
|
|
<span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Form</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">createElement</span><span class="p">(</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Row</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">createElement</span><span class="p">(</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Label</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">createElement</span><span class="p">(</span><span class="nx">Form</span><span class="p">.</span><span class="nx">Input</span><span class="p">,</span> <span class="kc">null</span><span class="p">)</span>
|
|
<span class="p">)</span>
|
|
<span class="p">)</span>
|
|
<span class="p">);</span>
|
|
</code></pre></div>
|
|
<blockquote>
|
|
<p>Note:</p>
|
|
|
|
<p>This feature is available in <a href="/react/blog/2014/07/17/react-v0.11.html#jsx">v0.11</a> and above.</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="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">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span>
|
|
<span class="nx">Person</span><span class="p">,</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>
|
|
<span class="p">);</span>
|
|
</code></pre></div><h3><a class="anchor" name="boolean-attributes"></a>Boolean Attributes <a class="hash-link" href="#boolean-attributes">#</a></h3>
|
|
<p>Omitting the value of an attribute causes JSX to treat it as <code>true</code>. To pass <code>false</code> an attribute expression must be used. This often comes up when using HTML form elements, with attributes like <code>disabled</code>, <code>required</code>, <code>checked</code> and <code>readOnly</code>.</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// These two are equivalent in JSX for disabling a button</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="nx">disabled</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="nx">disabled</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>
|
|
|
|
<span class="c1">// And these two are equivalent in JSX for not disabling a button</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"button"</span> <span class="nx">disabled</span><span class="o">=</span><span class="p">{</span><span class="kc">false</span><span class="p">}</span> <span class="o">/></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="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">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</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">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Nav</span><span class="p">)</span> <span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createElement</span><span class="p">(</span><span class="nx">Login</span><span class="p">)</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="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>
|
|
<blockquote>
|
|
<p>NOTE:</p>
|
|
|
|
<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>
|
|
</blockquote>
|
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