Weird HTML5 Worker JavaScript code (messages)

Question

https://github.com/daaain/JSSoundRecorder/blob/1c71ad46ab9088f92bc0a087dcb84df356b805f6/js/lib/recorderWorker.js

In lines 42 and 47 there are posted messages.

But these messages do not have a command field as required by the handlers in lines 5-23.

So I don't understand how these messages are handled. Please explain.

Answer 1

Those messages are sent to the main thread, not the worker itself. They represent results. That function doesn’t handle any of those outgoing messages. It only handles incoming messages. That’s what a function listening for message events does.

For example:

// Main thread:
var worker = new Worker("recorderWorker.js");
worker.postMessage({
  command: "init", // This is where the command property is required.
  config: …
});