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Paul O’Shannessy 2aa83f71cc v0.11.1
2014-07-25 11:25:07 -07:00

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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/09.8-perf.md" target="_blank">Edit on GitHub</a>
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<p>React is usually quite fast out of the box. However, in situations where you need to squeeze every ounce of performance out of your app, it provides a <a href="/react/docs/component-specs.html#updating-shouldcomponentupdate">shouldComponentUpdate</a> hook where you can add optimization hints to React&#39;s diff algorithm.</p>
<p>In addition to giving you an overview of your app&#39;s overall performance, ReactPerf is a profiling tool that tells you exactly where you need to put these hooks.</p>
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<p>Note:</p>
<p>The dev build of React is slower than the prod build, due to all the extra logic for providing, for example, React&#39;s friendly console warnings (stripped away in the prod build). Therefore, the profiler only serves to indicate the <em>relatively</em> expensive parts of your app.</p>
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<h2><a class="anchor" name="general-api"></a>General API <a class="hash-link" href="#general-api">#</a></h2>
<p>The <code>Perf</code> object documented here is exposed as <code>React.addons.Perf</code> when using the <code>react-with-addons.js</code> build in development mode.</p>
<h3><a class="anchor" name="perf.start-and-perf.stop"></a><code>Perf.start()</code> and <code>Perf.stop()</code> <a class="hash-link" href="#perf.start-and-perf.stop">#</a></h3>
<p>Start/stop the measurement. The React operations in-between are recorded for analyses below. Operations that took an insignificant amount of time are ignored.</p>
<h3><a class="anchor" name="perf.printinclusivemeasurements"></a><code>Perf.printInclusive(measurements)</code> <a class="hash-link" href="#perf.printinclusivemeasurements">#</a></h3>
<p>Prints the overall time taken. If no argument&#39;s passed, defaults to all the measurements from the last recording. This prints a nicely formatted table in the console, like so:</p>
<p><img src="/react/img/docs/perf-inclusive.png" alt=""></p>
<h3><a class="anchor" name="perf.printexclusivemeasurements"></a><code>Perf.printExclusive(measurements)</code> <a class="hash-link" href="#perf.printexclusivemeasurements">#</a></h3>
<p>&quot;Exclusive&quot; times don&#39;t include the times taken to mount the components: processing props, <code>getInitialState</code>, call <code>componentWillMount</code> and <code>componentDidMount</code>, etc.</p>
<p><img src="/react/img/docs/perf-exclusive.png" alt=""></p>
<h3><a class="anchor" name="perf.printwastedmeasurements"></a><code>Perf.printWasted(measurements)</code> <a class="hash-link" href="#perf.printwastedmeasurements">#</a></h3>
<p><strong>The most useful part of the profiler</strong>.</p>
<p>&quot;Wasted&quot; time is spent on components that didn&#39;t actually render anything, e.g. the render stayed the same, so the DOM wasn&#39;t touched.</p>
<p><img src="/react/img/docs/perf-wasted.png" alt=""></p>
<h3><a class="anchor" name="perf.printdommeasurements"></a><code>Perf.printDOM(measurements)</code> <a class="hash-link" href="#perf.printdommeasurements">#</a></h3>
<p>Prints the underlying DOM manipulations, e.g. &quot;set innerHTML&quot; and &quot;remove&quot;.</p>
<p><img src="/react/img/docs/perf-dom.png" alt=""></p>
<h2><a class="anchor" name="advanced-api"></a>Advanced API <a class="hash-link" href="#advanced-api">#</a></h2>
<p>The above print methods use <code>Perf.getLastMeasurements()</code> to pretty-print the result.</p>
<h3><a class="anchor" name="perf.getlastmeasurements"></a><code>Perf.getLastMeasurements()</code> <a class="hash-link" href="#perf.getlastmeasurements">#</a></h3>
<p>Get the measurements array from the last start-stop session. The array contains objects, each of which looks like this:</p>
<div class="highlight"><pre><code class="js language-js" data-lang="js"><span class="p">{</span>
<span class="c1">// The term &quot;inclusive&quot; and &quot;exclusive&quot; are explained below</span>
<span class="s2">&quot;exclusive&quot;</span><span class="o">:</span> <span class="p">{},</span>
<span class="c1">// &#39;.0.0&#39; is the React ID of the node</span>
<span class="s2">&quot;inclusive&quot;</span><span class="o">:</span> <span class="p">{</span><span class="s2">&quot;.0.0&quot;</span><span class="o">:</span> <span class="mf">0.0670000008540228</span><span class="p">,</span> <span class="s2">&quot;.0&quot;</span><span class="o">:</span> <span class="mf">0.3259999939473346</span><span class="p">},</span>
<span class="s2">&quot;render&quot;</span><span class="o">:</span> <span class="p">{</span><span class="s2">&quot;.0&quot;</span><span class="o">:</span> <span class="mf">0.036999990697950125</span><span class="p">,</span> <span class="s2">&quot;.0.0&quot;</span><span class="o">:</span> <span class="mf">0.010000003385357559</span><span class="p">},</span>
<span class="c1">// Number of instances</span>
<span class="s2">&quot;counts&quot;</span><span class="o">:</span> <span class="p">{</span><span class="s2">&quot;.0&quot;</span><span class="o">:</span> <span class="mi">1</span><span class="p">,</span> <span class="s2">&quot;.0.0&quot;</span><span class="o">:</span> <span class="mi">1</span><span class="p">},</span>
<span class="c1">// DOM touches</span>
<span class="s2">&quot;writes&quot;</span><span class="o">:</span> <span class="p">{},</span>
<span class="c1">// Extra debugging info</span>
<span class="s2">&quot;displayNames&quot;</span><span class="o">:</span> <span class="p">{</span>
<span class="s2">&quot;.0&quot;</span><span class="o">:</span> <span class="p">{</span><span class="s2">&quot;current&quot;</span><span class="o">:</span> <span class="s2">&quot;App&quot;</span><span class="p">,</span> <span class="s2">&quot;owner&quot;</span><span class="o">:</span> <span class="s2">&quot;&lt;root&gt;&quot;</span><span class="p">},</span>
<span class="s2">&quot;.0.0&quot;</span><span class="o">:</span> <span class="p">{</span><span class="s2">&quot;current&quot;</span><span class="o">:</span> <span class="s2">&quot;Box&quot;</span><span class="p">,</span> <span class="s2">&quot;owner&quot;</span><span class="o">:</span> <span class="s2">&quot;App&quot;</span><span class="p">}</span>
<span class="p">},</span>
<span class="s2">&quot;totalTime&quot;</span><span class="o">:</span> <span class="mf">0.48499999684281647</span>
<span class="p">}</span>
</code></pre></div>
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