@capacitor/background-runner

@capacitor/background-runner

Background Runner provides an event-based standalone JavaScript environment for executing your Javascript code outside of the web view.

Install

npm install @capacitor/background-runner
npx cap sync

Background Runner has support for various device APIs that require permission from the user prior to use.

iOS

On iOS you must enable the Background Modes capability.

Once added, you must enable the Background fetch and Background processing modes at a minimum to enable the ability to register and schedule your background tasks.

If you will be making use of Geolocation or Push Notifications, enable Location updates or Remote notifications respectively.

After enabling the Background Modes capability, add the following to your app's AppDelegate.swift:

At the top of the file, under import Capacitor add:

import CapacitorBackgroundRunner

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

    // ....
    BackgroundRunnerPlugin.registerBackgroundTask()
    BackgroundRunnerPlugin.handleApplicationDidFinishLaunching(launchOptions: launchOptions)
    // ....

    return true
}

To allow the Background Runner to handle remote notifications, add the following:

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
        // ....
        BackgroundRunnerPlugin.dispatchEvent(event: "remoteNotification", eventArgs: userInfo) { result in
            switch result {
            case .success:
                completionHandler(.newData)
            case .failure:
                completionHandler(.failed)
            }
        }
    }

Geolocation

Apple requires privacy descriptions to be specified in Info.plist for location information:

• NSLocationAlwaysUsageDescription (Privacy - Location Always Usage Description)
• NSLocationWhenInUseUsageDescription (Privacy - Location When In Use Usage Description)

Read about Configuring Info.plist in the iOS Guide for more information on setting iOS permissions in Xcode

Android

Insert the following line to android/app/build.gradle:

...

repositories {
    flatDir{
        dirs '../capacitor-cordova-android-plugins/src/main/libs', 'libs'
+		dirs '../../node_modules/@capacitor/background-runner/android/src/main/libs', 'libs'
    }
}
...

If you are upgrading from 1.0.5 with an existing Android project, be sure to delete the android-js-engine-release.aar from android/src/main/libs.

Geolocation

This API requires the following permissions be added to your AndroidManifest.xml:

<!-- Geolocation API -->
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-feature android:name="android.hardware.location.gps" />

The first two permissions ask for location data, both fine and coarse, and the last line is optional but necessary if your app requires GPS to function. You may leave it out, though keep in mind that this may mean your app is installed on devices lacking GPS hardware.

Local Notifications

Android 13 requires a permission check in order to send notifications. You are required to call checkPermissions() and requestPermissions() accordingly.

On Android 12 and older it won't show a prompt and will just return as granted.

Starting on Android 12, scheduled notifications won't be exact unless this permission is added to your AndroidManifest.xml:

<uses-permission android:name="android.permission.SCHEDULE_EXACT_ALARM" />

Note that even if the permission is present, users can still disable exact notifications from the app settings.

Read about Setting Permissions in the Android Guide for more information on setting Android permissions.

About Background Runner

During the course of building complex applications, its sometimes necessary to perform work while the application is not in the foreground. The challenge with standard Capacitor applications is that the webview is not available when these background events occur, requiring you to write native code to handle these events. This is where the Background Runner plugin comes in.

Background Runner makes it easy to write JavaScript code to handle native background events. All you need to do is create your runner JavaScript file and define your configuration, then the Background Runner plugin will automatically configure and schedule a native background task that will be executed according to your config and the rules of the platform. No modification to your UI code is necessary.

Using Background Runner

Background Runner contains a headless JavaScript environment that calls event handlers in javascript file that you designate in your capacitor.config.ts file. If the runner finds a event handler corresponding to incoming event in your runner file, it will execute the event handler, then shutdown once resolve() or reject() are called (or if the OS force kills your process).

Example Runner JS File

addEventListener('myCustomEvent', (resolve, reject, args) => {
  console.log('do something to update the system here');
  resolve();
});

addEventListener('myCustomEventWithReturnData', (resolve, reject, args) => {
  try {
    console.log('accepted this data: ' + JSON.stringify(args.user));

    const updatedUser = args.user;
    updatedUser.firstName = updatedUser.firstName + ' HELLO';
    updatedUser.lastName = updatedUser.lastName + ' WORLD';

    resolve(updatedUser);
  } catch (err) {
    reject(err);
  }
});

addEventListener('remoteNotification', (resolve, reject, args) => {
  try {
    console.log('received silent push notification');

    CapacitorNotifications.schedule([
      {
        id: 100,
        title: 'Enterprise Background Runner',
        body: 'Received silent push notification',
      },
    ]);

    resolve();
  } catch (err) {
    reject();
  }
});

Calling resolve() \ reject() is required within every event handler called by the runner. Failure to do this could result in your runner being killed by the OS if your event is called while the app is in the background. If the app is in the foreground, async calls to dispatchEvent may not resolve.

For more real world examples of using Background Runner, check out the Background Runner Test App.

Configuring Background Runner

On load, Background Runner will automatically register a background task that will be scheduled and run once your app is backgrounded.

Prop	Type	Description	Since
label	string	The name of the runner, used in logs.	1.0.0
src	string	The path to the runner JavaScript file, relative to the app bundle.	1.0.0
event	string	The name of the event that will be called when the OS executes the background task.	1.0.0
repeat	boolean	If background task should repeat based on the interval set in interval.	1.0.0
interval	number	The number of minutes after the the app is put into the background in which the background task should begin. If repeat is true, this also specifies the number of minutes between each execution.	1.0.0
autoStart	boolean	Automatically register and schedule background task on app load.	1.0.0

Examples

In capacitor.config.json:

{
  "plugins": {
    "BackgroundRunner": {
      "label": "com.example.background.task",
      "src": "runners/background.js",
      "event": "myCustomEvent",
      "repeat": true,
      "interval": 15,
      "autoStart": true
    }
  }
}

In capacitor.config.ts:

/// <reference types="@capacitor/background-runner" />

import { CapacitorConfig } from '@capacitor/cli';

const config: CapacitorConfig = {
  plugins: {
    BackgroundRunner: {
      label: "com.example.background.task",
      src: "runners/background.js",
      event: "myCustomEvent",
      repeat: true,
      interval: 15,
      autoStart: true,
    },
  },
};

export default config;

JavaScript API

Background Runner does not execute your Javascript code in a browser or web view, therefore the typical Web APIs you may be used to may not be available. This includes DOM APIs nor ability to interact with your application's DOM.

Below is a list of the available Web APIs provided in Background Runner:

• console
  • only info, log, warn, error , and debug are available
• TextDecoder
  • only decode is available
• TextEncoder
  • only encode is available
• addEventListener
  • Event Listener options and useCapture not supported
• setTimeout
• setInterval
• clearTimeout
• clearInterval
• crypto
• fetch
  • Request object not yet supported
  • Only method, headers and body supported in options object

In addition to the standard Web APIs, Background Runner also supports a number of custom Capacitor APIs custom APIs that expose relevant mobile device functionality

Runner Lifetimes

Currently, the runners are designed for performing periodic bursts of work while your app is in the background, or for executing asynchronous work in a thread separate from your UI while your app is in the foreground. As a result, runners are not long lived. State is not maintained between calls to events in the runner. Each call to dispatchEvent() creates a new context in which your runner code is loaded and executed, and once resolve() or reject() is called, the context is destroyed.

Android Battery Optimizations

Some Android vendors offer built-in battery optimization settings that go beyond what stock Android provides. Some of these optimizations must be disabled by your end users in order for your background tasks to work properly.

Visit Don't kill my app! for more information on the affected manufacturers and steps required by your users to adjust the settings.

Limitations of Background Tasks

It’s not possible to run persistent, always running background services on mobile operating systems. Due to the limitations imposed by iOS and Android designed to reduce battery and data consumption, background tasks are constrained with various limitations that you must keep in mind while designing and implementing your background task.

iOS

• Each invocation of your task has approximately up to 30 seconds of runtime before you must call completed() or your task is killed.
• While you can set an interval to define when your task runs after the app is backgrounded, or how often it should run, this is not guaranteed. iOS will determine when and how often you task will ultimately run, determined in part by how often you app is used.
• Background tasks are not executed in the simulator.

Android

• Your task has a maximum of 10 minutes to perform work, but to keep your task cross platform compatible, you should limit your work to 30 seconds at most.
• Repeating background tasks have a minimal interval of at least 15 minutes. Similar to iOS, any interval you request may not be hit exactly - actual execution time is subject to OS battery optimizations and other heuristics.

API

• checkPermissions()
• requestPermissions(...)
• dispatchEvent(...)
• Interfaces
• Type Aliases

checkPermissions()

checkPermissions() => any

Check permissions for the various Capacitor device APIs.

Returns: any

Since: 1.0.0

---

requestPermissions(...)

requestPermissions(options: RequestPermissionOptions) => any

Request permission to display local notifications.

Param	Type
options	RequestPermissionOptions

Returns: any

Since: 1.0.0

---

dispatchEvent(...)

dispatchEvent<T = void>(options: DispatchEventOptions) => any

Dispatches an event to the configured runner.

Param	Type
options	DispatchEventOptions

Returns: any

Since: 1.0.0

---

Interfaces

PermissionStatus

Prop	Type
geolocation	PermissionState
notifications	PermissionState

RequestPermissionOptions

Prop	Type
apis	{}

DispatchEventOptions

Prop	Type	Description	Since
label	string	The runner label to dispatch the event to	1.0.0
event	string	The name of the registered event listener.	1.0.0
details	{ [key: string]: any; }

Type Aliases

PermissionState

'prompt' | 'prompt-with-rationale' | 'granted' | 'denied'

API

'geolocation' | 'notifications'

Capacitor API

Interfaces

CapacitorDevice

Get information on the device, such as network connectivity and battery status.

Prop	Type	Description	Since
getBatteryStatus	() => BatteryStatus	Get the current battery status for the device.	1.0.0
getNetworkStatus	() => NetworkStatus	Get the current network status for the device.	1.0.0

BatteryStatus

Prop	Type
batteryLevel	number
isCharging	boolean

NetworkStatus

Prop	Type
connected	boolean
connectionType	string

CapacitorKV

A simple string key / value store backed by UserDefaults on iOS and Shared Preferences on Android.

Prop	Type	Description	Since
set	(key: string, value: string) => void	Set a string value with the given key.	1.0.0
get	(key: string) => { value: string; }	Get a string value for the given key.	1.0.0
remove	(key: string) => void	Remove a value with the given key.	1.0.0

CapacitorNotifications

Send basic local notifications.

Prop	Type	Description	Since
schedule	(options: {}) => void	Schedule a local notification	1.0.0

NotificationScheduleOptions

Prop	Type	Description	Since
id	number	The notification identifier. On Android it's a 32-bit int. So the value should be between -2147483648 and 2147483647 inclusive.	1.0.0
title	string	The title of the notification.	1.0.0
body	string	The body of the notification, shown below the title.	1.0.0
scheduleAt	Date	Date to send this notification.	1.0.0
sound	string	Name of the audio file to play when this notification is displayed. Include the file extension with the filename. On iOS, the file should be in the app bundle. On Android, the file should be in res/raw folder. Recommended format is .wav because is supported by both iOS and Android. Only available for iOS and Android < 26. For Android 26+ use channelId of a channel configured with the desired sound. If the sound file is not found, (i.e. empty string or wrong name) the default system notification sound will be used. If not provided, it will produce the default sound on Android and no sound on iOS.	1.0.0
actionTypeId	string	Associate an action type with this notification.	1.0.0
threadIdentifier	string	Used to group multiple notifications. Sets threadIdentifier on the UNMutableNotificationContent. Only available for iOS.	1.0.0
summaryArgument	string	The string this notification adds to the category's summary format string. Sets summaryArgument on the UNMutableNotificationContent. Only available for iOS.	1.0.0
group	string	Used to group multiple notifications. Calls setGroup() on NotificationCompat.Builder with the provided value. Only available for Android.	1.0.0
groupSummary	string	If true, this notification becomes the summary for a group of notifications. Calls setGroupSummary() on NotificationCompat.Builder with the provided value. Only available for Android when using group.	1.0.0
extra	any	Set extra data to store within this notification.	1.0.0
ongoing	boolean	If true, the notification can't be swiped away. Calls setOngoing() on NotificationCompat.Builder with the provided value. Only available for Android.	1.0.0
autoCancel	boolean	If true, the notification is canceled when the user clicks on it. Calls setAutoCancel() on NotificationCompat.Builder with the provided value. Only available for Android.	1.0.0
largeBody	string	Sets a multiline text block for display in a big text notification style.	1.0.0
summaryText	string	Used to set the summary text detail in inbox and big text notification styles. Only available for Android.	1.0.0
smallIcon	string	Set a custom status bar icon. If set, this overrides the smallIcon option from Capacitor configuration. Icons should be placed in your app's res/drawable folder. The value for this option should be the drawable resource ID, which is the filename without an extension. Only available for Android.	1.0.0
largeIcon	string	Set a large icon for notifications. Icons should be placed in your app's res/drawable folder. The value for this option should be the drawable resource ID, which is the filename without an extension. Only available for Android.	1.0.0
channelId	string	Specifies the channel the notification should be delivered on. If channel with the given name does not exist then the notification will not fire. If not provided, it will use the default channel. Calls setChannelId() on NotificationCompat.Builder with the provided value. Only available for Android 26+.	1.0.0

CapacitorGeolocation

Get access to device location information.

Prop	Type	Description	Since
getCurrentPosition	() => GetCurrentPositionResult	Get the device's last known location	1.0.0

GetCurrentPositionResult

Prop	Type	Description	Since
latitude	number	Latitude in decimal degrees	1.0.0
longitude	number	longitude in decimal degrees	1.0.0
accuracy	number	Accuracy level of the latitude and longitude coordinates in meters	1.0.0
altitude	number | null	The altitude the user is at (if available)	1.0.0
altitudeAccuracy	number | null	Accuracy level of the altitude coordinate in meters, if available. Available on all iOS versions and on Android 8.0+.	1.0.0
speed	number | null	The speed the user is traveling (if available)	1.0.0
heading	number | null	The heading the user is facing (if available)	1.0.0

CapcacitorWatch

Interact with a watch paired with this app

sendMessage, transferUserInfo and updateApplicationContext are raw routes to the WCSession delegate methods, but have no effects currently in a CapactiorWatch Watch application. They could be used if a native watch app is developed as a companion app to a Capacitor app

Prop	Type	Description
sendMessage	(options: []) => void	Sends a message to the watch with the sendMessage() WCSession delegate method This has no effect on a CapacitorWatch watch app
transferUserInfo	(options: []) => void	Sends information to the watch with the transferUserInfo() WCSession delegate method This has no effect on a CapacitorWatch watch app
updateApplicationContext	(options: []) => void	Updates the application context on the watch with the updateApplicationContext() WCSession delegate method This has no effect on a CapacitorWatch watch app
isReachable	boolean	Checks to see if the compaion watch is reachable
updateWatchUI	(options: { watchUI: string; }) => void	Replaces the current UI on the watch with what is specified here.
updateWatchData	(options: { data: { [key: string]: string; }; }) => void	Updates the data the watch is using to display variables in text and button fields