The postMessage()
method of the Client
interface allows a service worker to send a message to a client (a Window
, Worker
, or SharedWorker
). The message is received in the "message
" event on navigator.serviceWorker
.
Syntax
client.postMessage(message[, transfer]); client.postMessage(message[, { transfer }]);
Parameters
message
- The message to send to the client. This can be any structured-clonable type.
transfer
Optional- A sequence of objects that are transferred with the message. The ownership of these objects is given to the destination side and they are no longer usable on the sending side.
Return value
undefined
.
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. 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
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
postMessage | Chrome Full support 45 | Edge Full support ≤79 | Firefox
Full support
44
| IE No support No | Opera Full support 32 | Safari No support No | WebView Android Full support 45 | Chrome Android Full support 45 | Firefox Android Full support 44 | Opera Android Full support 32 | Safari iOS No support No | Samsung Internet Android Full support 5.0 |
Legend
- Full support
- Full support
- No support
- No support
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.
- See implementation notes.
- See implementation notes.