Client.postMessage

The Client.postMessage() method of the Client interface allows a service worker client to send a message to a ServiceWorker.

Syntax

Client.postMessage(message[, transfer]);

Returns

Void.

Parameters

message

The message to send to the service worker.

transfer Optional

A transferable object such as, for example, a reference to a port.

Examples

This code snippet is taken from the service worker post-message sample (see post-message live.) The code sends message data and transfers the port to the service worker so that it 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.

function sendMessage(message) {
  return new Promise(function(resolve, reject) {
     var messageChannel = new MessageChannel();
     messageChannel.port1.onmessage = function(event) {
       if (event.data.error) {
         reject(event.data.error);
       } else {
         resolve(event.data);
       }
     };
    navigator.serviceWorker.controller.postMessage(message, [messageChannel.port2]);
  });
}

Specifications

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

Browser compatibility

• [1] Behind a flag in Chrome 40 through 44.
• [2] Service workers (and Push) have been disabled in the Firefox 45 Extended Support Release (ESR.)