I am a newcomer to Javascript and web programming in general. I am trying to figure out web workers, and have the following code (running in chrome):
worker_example.html
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="worker_example.js"></script>
</head>
<html>
worker_example.js
var worker = new Worker("worker.js");
worker.addEventListener('message', function(e) {
document.write("hello");
}, false);
worker.postMessage("");
worker.js
// self.postMessage("");
My question is why doesn't worker.postMessage("") trigger the event? If I uncomment the single line in worker.js, however, everything works fine.
The event listener attached to worker listens for messages coming from the worker to the parent page. You need to register a listener in the worker as well.
parent.js
var worker = new Worker('worker.js');
worker.addEventListener('message', function (e) {
console.log(e.data);
});
worker.postMessage('marco');
worker.js
self.addEventListener('message', function (e) {
self.postMessage(e.data + ' polo');
});
来源：https://stackoverflow.com/questions/14328826/javascript-web-workers-why-do-i-need-to-postmessage-twice-to-trigger-event