This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The NavigatorWorker.sendBeacon() method can be used to asynchronously transfer a small amount of data over HTTP from a worker to a web server. This is functionally equivalent to the Navigator.sendBeacon() method; see that article for additional details on what this method can be used for and why.


self.navigator.sendBeacon(url, data);


The url parameter indicates the resolved URL to which the data is to be transmitted.
The data parameter is a ArrayBufferView, Blob, DOMString, or FormData object containing the data to be transmitted.

Return value

The sendBeacon() method returns true if the user agent can successfully queue the data for transfer, Otherwise it returns false.


The following example has two parts: first, the main thread creates a worker and sends it the message to forward to the server.

// Create a worker
var myWorker = new Worker('worker-beacon.js');

// Send the worker a message and set up a response callback

myWorker.postMessage('Send beacon!');

myWorker.onmessage = function(e) {
  var msg =;
  console.log('Worker beacon reply: ' + msg);

In the following code snippet, we see the worker's Worker.onmessage event handler. The text passed as the message data when calling Worker.postMessage() is accepted by the event handler and sent to the server by calling sendBeacon().

// Worker's onmessage handler

onmessage = function(ev) {
  var msg =;
  self.navigator.sendBeacon('', msg);


Specification Status Comment
The definition of 'sendBeacon()' in that specification.
Candidate Recommendation Initial definition

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support39 ? No No26 No
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support3939 ? No26 No4.0

See also

Document Tags and Contributors

Contributors to this page: fscholz, nmve, Sheppy, rolfedh, AFBarstow
Last updated by: fscholz,