Worker.postMessage()

Worker 接口的 postMessage()方法向worker的内部作用域发送一个消息。这接受单个参数，这是要发送给worker的数据。数据可以是由结构化克隆算法处理的任何值或JavaScript对象，其包括循环引用。

工作者可以使用 DedicatedWorkerGlobalScope.postMessage  方法将信息发送回生成它的线程。

Syntax

myWorker.postMessage(aMessage, transferList);

Parameters

aMessage

The object to deliver to the worker; this will be in the data field in the event delivered to the DedicatedWorkerGlobalScope.onmessage handler. This may be any value or JavaScript object handled by the structured clone algorithm, which includes cyclical references.

transferList 可选

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 becomes available only to the worker it was sent to.

Transferable objects are instances of classes like ArrayBuffer, MessagePort or ImageBitmap objects can be transferred. null is not an acceptable value for the transferList.

Returns

Void.

Example

The following code snippet shows the creation of a Worker object using the Worker() constructor. When either of two form inputs (first and second) have their values changed, change events invoke postMessage() to send the value of both inputs to the current worker.

var myWorker = new Worker('worker.js');
first.onchange = function() {
  myWorker.postMessage([first.value,second.value]);
  console.log('Message posted to worker');
}
second.onchange = function() {
  myWorker.postMessage([first.value,second.value]);
  console.log('Message posted to worker');
}

For a full example, see ourBasic dedicated worker example (run dedicated worker).

Transfer Example

This example shows a Firefox add-on that transfers an ArrayBuffer from the main thread to the ChromeWorker, and then the ChromeWorker transfers it back to the main thread.

Main thread code:

var myWorker = new ChromeWorker(self.path + 'myWorker.js');
function handleMessageFromWorker(msg) {
    console.log('incoming message from worker, msg:', msg);
    switch (msg.data.aTopic) {
        case 'do_sendMainArrBuff':
            sendMainArrBuff(msg.data.aBuf)
            break;
        default:
            throw 'no aTopic on incoming message to ChromeWorker';
    }
}
myWorker.addEventListener('message', handleMessageFromWorker);
// Ok lets create the buffer and send it
var arrBuf = new ArrayBuffer(8);
console.info('arrBuf.byteLength pre transfer:', arrBuf.byteLength);
myWorker.postMessage(
    {
        aTopic: 'do_sendWorkerArrBuff',
        aBuf: arrBuf // The array buffer that we passed to the transferrable section 3 lines below
    },
    [
        arrBuf // The array buffer we created 9 lines above
    ]
);
console.info('arrBuf.byteLength post transfer:', arrBuf.byteLength);

Worker code

self.onmessage = function (msg) {
    switch (msg.data.aTopic) {
        case 'do_sendWorkerArrBuff':
                sendWorkerArrBuff(msg.data.aBuf)
            break;
        default:
            throw 'no aTopic on incoming message to ChromeWorker';
    }
}
function sendWorkerArrBuff(aBuf) {
    console.info('from worker, PRE send back aBuf.byteLength:', aBuf.byteLength);    
    self.postMessage({aTopic:'do_sendMainArrBuff', aBuf:aBuf}, [aBuf]);
    console.info('from worker, POST send back aBuf.byteLength:', aBuf.byteLength);
}

Output logged

arrBuf.byteLength pre transfer: 8                              bootstrap.js:40
arrBuf.byteLength post transfer: 0                             bootstrap.js:42
from worker, PRE send back aBuf.byteLength: 8                  myWorker.js:5:2
incoming message from worker, msg: message { ... }             bootstrap.js:20
got back buf in main thread, aBuf.byteLength: 8                bootstrap.js:12
from worker, POST send back aBuf.byteLength: 0                 myWorker.js:7:2

byteLength goes to 0 as it is transferred. To see a full working example of this Firefox demo add-on see here: GitHub :: ChromeWorker - demo-transfer-arraybuffer

Specifications

Browser compatibility

[1] Internet Explorer does not support Transferable objects.

See also

• The Worker interface it belongs to.