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<html lang="en"><head><meta charset="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Headless JS · React Native</title><meta name="viewport" content="width=device-width"/><meta name="generator" content="Docusaurus"/><meta property="og:title" content="Headless JS · React Native"/><meta property="og:type" content="website"/><meta property="og:url" content="https://facebook.github.io/react-native/index.html"/><meta property="og:description" content="Headless JS is a way to run tasks in JavaScript while your app is in the background. It can be used, for example, to sync fresh data, handle push notifications, or play music."/><link rel="shortcut icon" href="/react-native/img/favicon.png"/><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/solarized-dark.min.css"/><link rel="alternate" type="application/atom+xml" href="https://facebook.github.io/blog/atom.xml" title="React Native Blog ATOM Feed"/><link rel="alternate" type="application/rss+xml" href="https://facebook.github.io/blog/feed.xml" title="React Native Blog RSS Feed"/><script type="text/javascript" src="https://snack.expo.io/embed.js"></script><script type="text/javascript" src="/react-native/js/codeblocks.js"></script><link rel="stylesheet" href="/react-native/css/main.css"/></head><body class="sideNavVisible doc"><div class="fixedHeaderContainer"><div class="headerWrapper wrapper"><header><a href="/react-native/"><img class="logo" 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href="/react-native/docs/keyboard.html">Keyboard</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/layout-props.html">Layout Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/layoutanimation.html">LayoutAnimation</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/linking.html">Linking</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/listviewdatasource.html">ListViewDataSource</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/netinfo.html">NetInfo</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/panresponder.html">PanResponder</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/permissionsandroid.html">PermissionsAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/pixelratio.html">PixelRatio</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/pushnotificationios.html">PushNotificationIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/settings.html">Settings</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/shadow-props.html">Shadow Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/share.html">Share</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/statusbarios.html">StatusBarIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/stylesheet.html">StyleSheet</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/systrace.html">Systrace</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/text-style-props.html">Text Style Props</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/timepickerandroid.html">TimePickerAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/toastandroid.html">ToastAndroid</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/transforms.html">Transforms</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/vibration.html">Vibration</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/vibrationios.html">VibrationIOS</a></li><li class="navListItem"><a class="navItem" href="/react-native/docs/view-style-props.html">View Style Props</a></li></ul></div></div></section></div><script>
var toggler = document.getElementById('navToggler');
var nav = document.getElementById('docsNav');
toggler.onclick = function() {
nav.classList.toggle('docsSliderActive');
};
</script></nav></div><div class="container mainContainer"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/facebook/react-native-website/blob/master/docs/headless-js-android.md" target="_blank">Edit</a><h1>Headless JS</h1></header><article><div><span><p>Headless JS is a way to run tasks in JavaScript while your app is in the background. It can be used, for example, to sync fresh data, handle push notifications, or play music.</p>
<h2><a class="anchor" aria-hidden="true" id="the-js-api"></a><a href="#the-js-api" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>The JS API</h2>
<p>A task is a simple async function that you register on <code>AppRegistry</code>, similar to registering React applications:</p>
<pre><code class="hljs css javascript">AppRegistry.registerHeadlessTask(<span class="hljs-string">'SomeTaskName'</span>, () =&gt; <span class="hljs-built_in">require</span>(<span class="hljs-string">'SomeTaskName'</span>));
</code></pre>
<p>Then, in <code>SomeTaskName.js</code>:</p>
<pre><code class="hljs css javascript"><span class="hljs-built_in">module</span>.exports = <span class="hljs-keyword">async</span> (taskData) =&gt; {
<span class="hljs-comment">// do stuff</span>
};
</code></pre>
<p>You can do anything in your task as long as it doesn't touch UI: network requests, timers and so on. Once your task completes (i.e. the promise is resolved), React Native will go into &quot;paused&quot; mode (unless there are other tasks running, or there is a foreground app).</p>
<h2><a class="anchor" aria-hidden="true" id="the-java-api"></a><a href="#the-java-api" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>The Java API</h2>
<p>Yes, this does still require some native code, but it's pretty thin. You need to extend <code>HeadlessJsTaskService</code> and override <code>getTaskConfig</code>, e.g.:</p>
<pre><code class="hljs css java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyTaskService</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">HeadlessJsTaskService</span> </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">protected</span> <span class="hljs-meta">@Nullable</span> <span class="hljs-function">HeadlessJsTaskConfig <span class="hljs-title">getTaskConfig</span><span class="hljs-params">(Intent intent)</span> </span>{
Bundle extras = intent.getExtras();
<span class="hljs-keyword">if</span> (extras != <span class="hljs-keyword">null</span>) {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> HeadlessJsTaskConfig(
<span class="hljs-string">"SomeTaskName"</span>,
Arguments.fromBundle(extras),
<span class="hljs-number">5000</span>, <span class="hljs-comment">// timeout for the task</span>
<span class="hljs-keyword">false</span> <span class="hljs-comment">// optional: defines whether or not the task is allowed in foreground. Default is false</span>
);
}
<span class="hljs-keyword">return</span> <span class="hljs-keyword">null</span>;
}
}
</code></pre>
<p>Then add the service to your <code>AndroidManifest.xml</code> file:</p>
<pre><code class="hljs">&lt;service android:<span class="hljs-built_in">name</span>=<span class="hljs-string">"com.example.MyTaskService"</span> /&gt;
</code></pre>
<p>Now, whenever you <a href="https://developer.android.com/reference/android/content/Context.html#startService(android.content.Intent)">start your service</a>, e.g. as a periodic task or in response to some system event / broadcast, JS will spin up, run your task, then spin down.</p>
<p>Example:</p>
<pre><code class="hljs css java">Intent service = <span class="hljs-keyword">new</span> Intent(getApplicationContext(), MyTaskService.class);
Bundle bundle = <span class="hljs-keyword">new</span> Bundle();
bundle.putString(<span class="hljs-string">"foo"</span>, <span class="hljs-string">"bar"</span>);
service.putExtras(bundle);
getApplicationContext().startService(service);
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="caveats"></a><a href="#caveats" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Caveats</h2>
<ul>
<li>By default, your app will crash if you try to run a task while the app is in the foreground. This is to prevent developers from shooting themselves in the foot by doing a lot of work in a task and slowing the UI. You can pass a fourth <code>boolean</code> argument to control this behaviour.</li>
<li>If you start your service from a <code>BroadcastReceiver</code>, make sure to call <code>HeadlessJsTaskService.acquireWakeLockNow()</code> before returning from <code>onReceive()</code>.</li>
</ul>
<h2><a class="anchor" aria-hidden="true" id="example-usage"></a><a href="#example-usage" aria-hidden="true" class="hash-link" ><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example Usage</h2>
<p>Service can be started from Java API. First you need to decide when the service should be started and implement your solution accordingly. Here is a simple example that reacts to network connection change.</p>
<p>Following lines shows part of Android manifest file for registering broadcast receiver.</p>
<pre><code class="hljs css xml"><span class="hljs-tag">&lt;<span class="hljs-name">receiver</span> <span class="hljs-attr">android:name</span>=<span class="hljs-string">".NetworkChangeReceiver"</span> &gt;</span>
<span class="hljs-tag">&lt;<span class="hljs-name">intent-filter</span>&gt;</span>
<span class="hljs-tag">&lt;<span class="hljs-name">action</span> <span class="hljs-attr">android:name</span>=<span class="hljs-string">"android.net.conn.CONNECTIVITY_CHANGE"</span> /&gt;</span>
<span class="hljs-tag">&lt;/<span class="hljs-name">intent-filter</span>&gt;</span>
<span class="hljs-tag">&lt;/<span class="hljs-name">receiver</span>&gt;</span>
</code></pre>
<p>Broadcast receiver then handles intent that was broadcasted in onReceive function. This is a great place to check whether your app is on foreground or not. If app is not on foreground we can prepare our intent to be started, with no information or additional information bundled using <code>putExtra</code> (keep in mind bundle can handle only parcelable values). In the end service is started and wakelock is acquired.</p>
<pre><code class="hljs css java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">NetworkChangeReceiver</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">BroadcastReceiver</span> </span>{
<span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onReceive</span><span class="hljs-params">(<span class="hljs-keyword">final</span> Context context, <span class="hljs-keyword">final</span> Intent intent)</span> </span>{
<span class="hljs-comment">/**
This part will be called everytime network connection is changed
e.g. Connected -&gt; Not Connected
**/</span>
<span class="hljs-keyword">if</span> (!isAppOnForeground((context))) {
<span class="hljs-comment">/**
We will start our service and send extra info about
network connections
**/</span>
<span class="hljs-keyword">boolean</span> hasInternet = isNetworkAvailable(context);
Intent serviceIntent = <span class="hljs-keyword">new</span> Intent(context, MyTaskService.class);
serviceIntent.putExtra(<span class="hljs-string">"hasInternet"</span>, hasInternet);
context.startService(serviceIntent);
HeadlessJsTaskService.acquireWakeLockNow(context);
}
}
<span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">isAppOnForeground</span><span class="hljs-params">(Context context)</span> </span>{
<span class="hljs-comment">/**
We need to check if app is in foreground otherwise the app will crash.
http://stackoverflow.com/questions/8489993/check-android-application-is-in-foreground-or-not
**/</span>
ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
List&lt;ActivityManager.RunningAppProcessInfo&gt; appProcesses =
activityManager.getRunningAppProcesses();
<span class="hljs-keyword">if</span> (appProcesses == <span class="hljs-keyword">null</span>) {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">false</span>;
}
<span class="hljs-keyword">final</span> String packageName = context.getPackageName();
<span class="hljs-keyword">for</span> (ActivityManager.RunningAppProcessInfo appProcess : appProcesses) {
<span class="hljs-keyword">if</span> (appProcess.importance ==
ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND &amp;&amp;
appProcess.processName.equals(packageName)) {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">true</span>;
}
}
<span class="hljs-keyword">return</span> <span class="hljs-keyword">false</span>;
}
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">isNetworkAvailable</span><span class="hljs-params">(Context context)</span> </span>{
ConnectivityManager cm = (ConnectivityManager)
context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
<span class="hljs-keyword">return</span> (netInfo != <span class="hljs-keyword">null</span> &amp;&amp; netInfo.isConnected());
}
}
</code></pre>
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