Web/API/DedicatedWorkerGlobalScope/postMessage
The postMessage()
method of the DedicatedWorkerGlobalScope
interface sends a message to the main thread that spawned it. This accepts a single parameter, which is the data to send to the worker. The data may be any value or JavaScript object handled by the structured clone algorithm, which includes cyclical references.
The main scope that spawned the worker can send back information to the thread that spawned it using the Worker.postMessage
method.
Syntax
postMessage(aMessage, transferList);
Parameters
- aMessage
- The object to deliver to the main thread; this will be in the data field in the event delivered to the
Worker.onmessage
handler. This may be any value or JavaScript object handled by the structured clone algorithm, which includes cyclical references. - transferList Optional
- An optional array of
Transferable
objects to transfer ownership of. If the ownership of an object is transferred, it becomes unusable (neutered) in the context it was sent from and it becomes available only to the main thread it was sent to. - Only
MessagePort
andArrayBuffer
objects can be transferred.
Returns
Void.
Example
The following code snippet shows worker.js
, in which an onmessage
handler is used to handle messages from the main script. Inside the handler a calculation is done from which a result message is created; this is then sent back to the main thread using postMessage(workerResult);
onmessage = function(e) {
console.log('Message received from main script');
var workerResult = 'Result: ' + (e.data[0] * e.data[1]);
console.log('Posting message back to main script');
postMessage(workerResult);
}
In the main script, onmessage
would have to be called on a Worker object
, whereas inside the worker script you just need onmessage
because the worker is effectively the global scope (DedicatedWorkerGlobalScope
).
For a full example, see ourBasic dedicated worker example ([[../../../../../../../mdn.github.io/simple-web-worker/index|run dedicated worker]]).
Note: postMessage()
can only send a single object at once. As seen above, if you want to pass multiple values you can send an array.
Specifications
Specification | Status | Comment |
HTML Living StandardThe definition of 'DedicatedWorkerGlobalScope.postMessage()' in that specification. | Living Standard |
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.
Update compatibility data on GitHub
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
postMessage
|
Chrome
Full support 4 |
Edge
Full support 12 |
Firefox
Full support 3.5 |
IE
Full support 10 |
Opera
Full support 10.6 |
Safari
Full support 4 |
WebView Android
Full support Yes |
Chrome Android
Full support Yes |
Firefox Android
Full support 4 |
Opera Android
Full support 11 |
Safari iOS
Full support 5.1 |
Samsung Internet Android
Full support Yes |
Legend
- Full support
- Full support
See also
The DedicatedWorkerGlobalScope
interface it belongs to.
DedicatedWorkerGlobalScope.postMessage() by Mozilla Contributors is licensed under CC-BY-SA 2.5.