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 (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 |
---|---|---|
WHATWG HTML Living Standard The definition of 'DedicatedWorkerGlobalScope.postMessage()' in that specification. |
Living Standard |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 4 | 3.5 (1.9.1) | 10 | 10.6 | 4 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | Firefox OS (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|
Basic support | ? | (Yes) | 1.0 (1.9.1) | 1.0.1 | 10 | 11.5 | 5.1 |
See also
The DedicatedWorkerGlobalScope
interface it belongs to.