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Dan Abramov
523 lines
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HTML
523 lines
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<div class="inner-content">
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/02.3-jsx-gotchas.md" target="_blank">Edit on GitHub</a>
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<h1>
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JSX Gotchas
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</h1>
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<div class="subHeader"></div>
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<p>JSX looks like HTML but there are some important differences you may run into.</p>
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<blockquote>
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<p>Note:</p>
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<p>For DOM differences, such as the inline <code>style</code> attribute, check <a href="/react/docs/dom-differences.html">here</a>.</p>
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</blockquote>
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<h2><a class="anchor" name="html-entities"></a>HTML Entities <a class="hash-link" href="#html-entities">#</a></h2>
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<p>You can insert HTML entities within literal text in JSX:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="nx">First</span> <span class="o">&</span><span class="nx">middot</span><span class="p">;</span> <span class="nx">Second</span><span class="o"><</span><span class="err">/div></span>
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</code></pre></div>
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<p>If you want to display an HTML entity within dynamic content, you will run into double escaping issues as React escapes all the strings you are displaying in order to prevent a wide range of XSS attacks by default.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="c1">// Bad: It displays "First &middot; Second"</span>
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<span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="p">{</span><span class="s1">'First &middot; Second'</span><span class="p">}</span><span class="o"><</span><span class="err">/div></span>
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</code></pre></div>
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<p>There are various ways to work-around this issue. The easiest one is to write Unicode characters directly in JavaScript. You need to make sure that the file is saved as UTF-8 and that the proper UTF-8 directives are set so the browser will display it correctly.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="p">{</span><span class="s1">'First · Second'</span><span class="p">}</span><span class="o"><</span><span class="err">/div></span>
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</code></pre></div>
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<p>A safer alternative is to find the <a href="http://www.fileformat.info/info/unicode/char/b7/index.htm">unicode number corresponding to the entity</a> and use it inside of a JavaScript string.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="p">{</span><span class="s1">'First \u00b7 Second'</span><span class="p">}</span><span class="o"><</span><span class="err">/div></span>
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<span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="p">{</span><span class="s1">'First '</span> <span class="o">+</span> <span class="nb">String</span><span class="p">.</span><span class="nx">fromCharCode</span><span class="p">(</span><span class="mi">183</span><span class="p">)</span> <span class="o">+</span> <span class="s1">' Second'</span><span class="p">}</span><span class="o"><</span><span class="err">/div></span>
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</code></pre></div>
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<p>You can use mixed arrays with strings and JSX elements. Each JSX element in the array needs a unique key.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="p">{[</span><span class="s1">'First '</span><span class="p">,</span> <span class="o"><</span><span class="nx">span</span> <span class="nx">key</span><span class="o">=</span><span class="s2">"middot"</span><span class="o">>&</span><span class="nx">middot</span><span class="p">;</span><span class="o"><</span><span class="err">/span>, ' Second']}</div></span>
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</code></pre></div>
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<p>As a last resort, you always have the ability to <a href="/react/tips/dangerously-set-inner-html.html">insert raw HTML</a>.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">div</span> <span class="nx">dangerouslySetInnerHTML</span><span class="o">=</span><span class="p">{{</span><span class="nx">__html</span><span class="o">:</span> <span class="s1">'First &middot; Second'</span><span class="p">}}</span> <span class="o">/></span>
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</code></pre></div><h2><a class="anchor" name="custom-html-attributes"></a>Custom HTML Attributes <a class="hash-link" href="#custom-html-attributes">#</a></h2>
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<p>If you pass properties to native HTML elements that do not exist in the HTML specification, React will not render them. If you want to use a custom attribute, you should prefix it with <code>data-</code>.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">div</span> <span class="nx">data</span><span class="o">-</span><span class="nx">custom</span><span class="o">-</span><span class="nx">attribute</span><span class="o">=</span><span class="s2">"foo"</span> <span class="o">/></span>
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</code></pre></div>
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<p>However, arbitrary attributes are supported on custom elements (those with a hyphen in the tag name or an <code>is="..."</code> attribute).</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">x</span><span class="o">-</span><span class="nx">my</span><span class="o">-</span><span class="nx">component</span> <span class="nx">custom</span><span class="o">-</span><span class="nx">attribute</span><span class="o">=</span><span class="s2">"foo"</span> <span class="o">/></span>
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</code></pre></div>
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<p><a href="http://www.w3.org/WAI/intro/aria">Web Accessibility</a> attributes starting with <code>aria-</code> will be rendered properly.</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">div</span> <span class="nx">aria</span><span class="o">-</span><span class="nx">hidden</span><span class="o">=</span><span class="p">{</span><span class="kc">true</span><span class="p">}</span> <span class="o">/></span>
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</code></pre></div>
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