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<!DOCTYPE html><html><head><title>Systrace</title><meta charset="utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta name="viewport" content="width=device-width"><meta property="fb:app_id" content="1677033832619985"><meta property="fb:admins" content="121800083"><meta property="og:site_name" content="React Native"><meta property="og:title" content="Systrace"><meta property="og:url" content="https://facebook.github.io/react-native/index.html"><meta property="og:image" content="https://facebook.github.io/react-native/img/opengraph.png"><meta property="og:description" content="A framework for building native apps using React"><meta name="twitter:site" content="@reactnative"><meta name="twitter:card" content="summary_large_image"><meta property="og:type" content="website"><base href="/react-native/"><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"><link rel="shortcut icon" href="img/favicon.png?2"><link rel="stylesheet" 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href="docs/imagepickerios.html">ImagePickerIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/imagestore.html">ImageStore</a></li><li><a style="margin-left:10px;" class="" href="docs/interactionmanager.html">InteractionManager</a></li><li><a style="margin-left:10px;" class="" href="docs/keyboard.html">Keyboard</a></li><li><a style="margin-left:10px;" class="" href="docs/layoutanimation.html">LayoutAnimation</a></li><li><a style="margin-left:10px;" class="" href="docs/linking.html">Linking</a></li><li><a style="margin-left:10px;" class="" href="docs/nativemethodsmixin.html">NativeMethodsMixin</a></li><li><a style="margin-left:10px;" class="" href="docs/netinfo.html">NetInfo</a></li><li><a style="margin-left:10px;" class="" href="docs/panresponder.html">PanResponder</a></li><li><a style="margin-left:10px;" class="" href="docs/permissionsandroid.html">PermissionsAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/pixelratio.html">PixelRatio</a></li><li><a style="margin-left:10px;" class="" href="docs/pushnotificationios.html">PushNotificationIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/settings.html">Settings</a></li><li><a style="margin-left:10px;" class="" href="docs/share.html">Share</a></li><li><a style="margin-left:10px;" class="" href="docs/statusbarios.html">StatusBarIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/stylesheet.html">StyleSheet</a></li><li><a style="margin-left:10px;" class="active" href="docs/systrace.html">Systrace</a></li><li><a style="margin-left:10px;" class="" href="docs/timepickerandroid.html">TimePickerAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/toastandroid.html">ToastAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/vibration.html">Vibration</a></li><li><a style="margin-left:10px;" class="" href="docs/vibrationios.html">VibrationIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/layout-props.html">Layout Props</a></li><li><a style="margin-left:10px;" class="" href="docs/shadow-props.html">Shadow Props</a></li></ul></div></div></div><div class="inner-content"><a id="content"></a><h1><a class="anchor" name="systrace"></a>Systrace <a class="hash-link" href="docs/systrace.html#systrace">#</a></h1><div><div></div><span><h3><a class="anchor" name="methods"></a>Methods <a class="hash-link" href="docs/systrace.html#methods">#</a></h3><div class="props"><div class="prop"><h4 class="methodTitle"><a class="anchor" name="setenabled"></a><span class="methodType">static </span>setEnabled<span class="methodType">(enabled)</span> <a class="hash-link" href="docs/systrace.html#setenabled">#</a></h4></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="isenabled"></a><span class="methodType">static </span>isEnabled<span class="methodType">()</span> <a class="hash-link" href="docs/systrace.html#isenabled">#</a></h4></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="beginevent"></a><span class="methodType">static </span>beginEvent<span class="methodType">(profileName?, args?)</span> <a class="hash-link" href="docs/systrace.html#beginevent">#</a></h4><div><p>beginEvent/endEvent for starting and then ending a profile within the same call stack frame</p></div></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="endevent"></a><span class="methodType">static </span>endEvent<span class="methodType">()</span> <a class="hash-link" href="docs/systrace.html#endevent">#</a></h4></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="beginasyncevent"></a><span class="methodType">static </span>beginAsyncEvent<span class="methodType">(profileName?)</span> <a class="hash-link" href="docs/systrace.html#beginasyncevent">#</a></h4><div><p>beginAsyncEvent/endAsyncEvent for starting and then ending a profile where the end can either
occur on another thread or out of the current stack frame, eg await
the returned cookie variable should be used as input into the endAsyncEvent call to end the profile</p></div></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="endasyncevent"></a><span class="methodType">static </span>endAsyncEvent<span class="methodType">(profileName?, cookie?)</span> <a class="hash-link" href="docs/systrace.html#endasyncevent">#</a></h4></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="counterevent"></a><span class="methodType">static </span>counterEvent<span class="methodType">(profileName?, value?)</span> <a class="hash-link" href="docs/systrace.html#counterevent">#</a></h4><div><p>counterEvent registers the value to the profileName on the systrace timeline</p></div></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="attachtorelayprofiler"></a><span class="methodType">static </span>attachToRelayProfiler<span class="methodType">(relayProfiler)</span> <a class="hash-link" href="docs/systrace.html#attachtorelayprofiler">#</a></h4><div><p>Relay profiles use await calls, so likely occur out of current stack frame
therefore async variant of profiling is used</p></div></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="swizzlejson"></a><span class="methodType">static </span>swizzleJSON<span class="methodType">()</span> <a class="hash-link" href="docs/systrace.html#swizzlejson">#</a></h4><div><p>This is not called by default due to perf overhead but it&#x27;s useful
if you want to find traces which spend too much time in JSON.</p></div></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="measuremethods"></a><span class="methodType">static </span>measureMethods<span class="methodType">(object, objectName, methodNames)</span> <a class="hash-link" href="docs/systrace.html#measuremethods">#</a></h4><div><p>Measures multiple methods of a class. For example, you can do:
Systrace.measureMethods(JSON, &#x27;JSON&#x27;, [&#x27;parse&#x27;, &#x27;stringify&#x27;]);</p><p>@param object
@param objectName
@param methodNames Map from method names to method display names.</p></div></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="measure"></a><span class="methodType">static </span>measure<span class="methodType">(objName, fnName, func)</span> <a class="hash-link" href="docs/systrace.html#measure">#</a></h4><div><p>Returns an profiled version of the input function. For example, you can:
JSON.parse = Systrace.measure(&#x27;JSON&#x27;, &#x27;parse&#x27;, JSON.parse);</p><p>@param objName
@param fnName
@param {function} func
@return {function} replacement function</p></div></div></div></span></div><p class="edit-page-block">You can <a target="_blank" href="https://github.com/facebook/react-native/blob/master/Libraries/Performance/Systrace.js">edit the content above on GitHub</a> and send us a pull request!</p><div class="docs-prevnext"><a class="docs-prev" href="docs/stylesheet.html#content">← Prev</a><a class="docs-next" href="docs/timepickerandroid.html#content">Next →</a></div></div></section><footer class="nav-footer"><section class="sitemap"><a href="/react-native" class="nav-home"><img src="img/header_logo.png" alt="React Native" width="66" height="58"></a><div><h5><a href="docs/">Docs</a></h5><a href="docs/getting-started.html">Getting Started</a><a href="docs/tutorial.html">Tutorial</a><a href="docs/integration-with-existing-apps.html">Integration With Existing Apps</a><a href="docs/more-resources.html">More Resources</a></div><div><h5><a href="/react-native/support.html">Community</a></h5><a href="/react-native/showcase.html">Showcase</a><a href="http://www.meetup.com/topics/react-native/" target="_blank">Upcoming Events</a><a href="https://www.facebook.com/groups/react.native.community" target="_blank">Facebook Group</a><a href="https://twitter.com/reactnative" target="_blank">Twitter</a></div><div><h5><a href="/react-native/support.html">Help</a></h5><a href="http://stackoverflow.com/questions/tagged/react-native" target="_blank">Stack Overflow</a><a href="https://discord.gg/0ZcbPKXt5bZjGY5n">Reactiflux Chat</a><a href="/react-native/versions.html" target="_blank">Latest Releases</a><a href="https://react-native.canny.io/feature-requests" target="_blank">Feature Requests</a></div><div><h5>More</h5><a href="/react-native/blog">Blog</a><a href="https://github.com/facebook/react-native" target="_blank">GitHub</a><a href="http://facebook.github.io/react/" target="_blank">React</a></div></section><section class="newsletter"><div id="mc_embed_signup"><form action="//reactnative.us10.list-manage.com/subscribe/post?u=db0dd948e2b729ee62625b1a8&amp;id=47cd41008f" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate><div id="mc_embed_signup_scroll"><label for="mce-EMAIL"><h5>Get the React Native Newsletter</h5></label><input type="email" value="" name="EMAIL" class="email" id="mce-EMAIL" placeholder="email address" required><div style="position:absolute;left:-5000px;" aria-hidden="true"><input type="text" name="b_db0dd948e2b729ee62625b1a8_47cd41008f" tabindex="-1" value=""></div><div class="clear"><input type="submit" value="Sign up" name="subscribe" id="mc-embedded-subscribe" class="button"></div></div></form></div></section><a href="https://code.facebook.com/projects/" target="_blank" class="fbOpenSource"><img src="img/oss_logo.png" alt="Facebook Open Source" width="170" height="45"></a><section class="copyright">Copyright © 2017 Facebook Inc.</section></footer></div><div id="fb-root"></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><script>
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