This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The Client interface of the ServiceWorker API represents the scope of a service worker client. A service worker client is either a document in a browser context or a SharedWorker, which is controlled by an active worker. A client object acts as a snapshot representation of its associated service worker client in the scope of a service worker.


Allows a service worker to send a message to a ServiceWorkerClient.


Client.frameType Read only
Indicates the type of browsing context of the current client. This value can be one of auxiliarytop-levelnested, or none. Read only
Returns the universally unique identifier of the Client object.
Client.url Read only
The URL of the current service worker client.


This code is based on a snippet taken from the service worker post-message sample (see post-message live.) The code sends message data to which the service worker can reply via Client.postMessage().

The message is wrapped in a promise that resolves if the response doesn't contain an error and rejects with the error.

// service worker client (e.g. a document)
function sendMessage(message) {
  return new Promise(function(resolve, reject) {
    // note that this is the ServiceWorker.postMessage version
    window.serviceWorker.onMessage = function(e) {

// controlling service worker
self.addEventListener("message", function(e) {
  // e.source is a client object
  e.source.postMessage("Hello! Your message was: " +;


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

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 40.0[1] 44.0 (44.0)[2] No support ? No support
Feature Android Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support ? 44.0 (44.0) ? No support ? No support ?

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Client Experimental Interface Reference Service Workers ServiceWorkerClient ServiceWorkers