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react/docs/class-name-manipulation.html
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<h1>Class Name Manipulation</h1>
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<p><code>classSet()</code> is a neat utility for easily manipulating the DOM <code>class</code> string.</p>
<p>Here&#39;s a common scenario and its solution without <code>classSet()</code>:</p>
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="c1">// inside some `&lt;Message /&gt;` React component</span>
<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">classString</span> <span class="o">=</span> <span class="s1">&#39;message&#39;</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">isImportant</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">classString</span> <span class="o">+=</span> <span class="s1">&#39; message-important&#39;</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">if</span> <span class="p">(</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">isRead</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">classString</span> <span class="o">+=</span> <span class="s1">&#39; message-read&#39;</span><span class="p">;</span>
<span class="p">}</span>
<span class="c1">// &#39;message message-important message-read&#39;</span>
<span class="k">return</span> <span class="o">&lt;</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="p">{</span><span class="nx">classString</span><span class="p">}</span><span class="o">&gt;</span><span class="nx">Great</span><span class="p">,</span> <span class="nx">I</span><span class="err">&#39;</span><span class="nx">ll</span> <span class="nx">be</span> <span class="nx">there</span><span class="p">.</span><span class="o">&lt;</span><span class="err">/div&gt;;</span>
<span class="p">}</span>
</code></pre></div>
<p>This can quickly get tedious, as assigning class name strings can be hard to read and error-prone. <code>classSet()</code> solves this problem:</p>
<div class="highlight"><pre><code class="javascript language-javascript" data-lang="javascript"><span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">cx</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">addons</span><span class="p">.</span><span class="nx">classSet</span><span class="p">;</span>
<span class="kd">var</span> <span class="nx">classes</span> <span class="o">=</span> <span class="nx">cx</span><span class="p">({</span>
<span class="s1">&#39;message&#39;</span><span class="o">:</span> <span class="kc">true</span><span class="p">,</span>
<span class="s1">&#39;message-important&#39;</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">isImportant</span><span class="p">,</span>
<span class="s1">&#39;message-read&#39;</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">isRead</span>
<span class="p">});</span>
<span class="c1">// same final string, but much cleaner</span>
<span class="k">return</span> <span class="o">&lt;</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="p">{</span><span class="nx">classes</span><span class="p">}</span><span class="o">&gt;</span><span class="nx">Great</span><span class="p">,</span> <span class="nx">I</span><span class="err">&#39;</span><span class="nx">ll</span> <span class="nx">be</span> <span class="nx">there</span><span class="p">.</span><span class="o">&lt;</span><span class="err">/div&gt;;</span>
<span class="p">}</span>
</code></pre></div>
<p>When using <code>classSet()</code>, pass an object with keys of the CSS class names you might or might not need. Truthy values will result in the key being a part of the resulting string.</p>
<p>No more hacky string concatenations!</p>
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