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

The postMessage() method of Client allows a service worker to send a message to a client (a WindowWorker, or SharedWorker). The message is received in the "message" event on navigator.serviceWorker

Syntax

Client.postMessage(message[, transfer]);

Parameters

message
The message to send to the service worker. This can be any structured-clonable type.
transfer Optional
A sequence of objects to transfer. These objects must also be present in the message.

Return value

Void.

Examples

Sending a message from a service worker to a client:

addEventListener('fetch', event => {
  event.waitUntil(async function() {
    // Exit early if we don't have access to the client.
    // Eg, if it's cross-origin.
    if (!event.clientId) return;

    // Get the client.
    const client = await clients.get(event.clientId);
    // Exit early if we don't get the client.
    // Eg, if it closed.
    if (!client) return;

    // Send a message to the client.
    self.clients.matchAll().then(function (clients){
      clients.forEach(function(client){
        client.postMessage({
          msg: "Hey I just got a fetch from you!",
          url: event.request.url
        });
      });
    });
   
  }());
});

Receiving that message:

navigator.serviceWorker.addEventListener('message', event => {
  console.log(event.data.msg, event.data.url);
});

Specifications

Specification Status Comment
Service Workers
The definition of 'postMessage()' in that specification.
Working Draft Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic support
Experimental
Chrome Full support 45Edge ? Firefox Full support 44
Notes
Full support 44
Notes
Notes Service workers (and Push) have been disabled in the Firefox 45 & 52 Extended Support Releases (ESR).
IE No support NoOpera Full support 32Safari No support NoWebView Android Full support 45Chrome Android Full support 45Edge Mobile No support NoFirefox Android Full support 44Opera Android Full support 32Safari iOS No support NoSamsung Internet Android Full support 5.0

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
See implementation notes.
See implementation notes.

Document Tags and Contributors

Last updated by: RonRoyston,