HTML5 WebWorker Logic flow

Question

So I have this main js file:

var worker = new Worker("../Scripts/worker.js");
worker.onmessage = function (event) {
    alert("Worker said : " + event.data);
};
worker.postMessage("Naruto");
worker.postMessage("Sakura");

and worker.js is here:

self.onmessage = function (event) {
      self.postMessage("Hi " + event.data);
};

self.postMessage("WHERE'S SASUKE? [1]");
self.postMessage("WHERE'S SASUKE? [2]");

I'm still a little bit confused on how they actually work. But what comes out is this (in order of appearance):

Worker said: WHERE'S SASUKE? [1]
Worker said: WHERE'S SASUKE? [2]
Worker said: Hi Naruto
Worker said: Hi Sakura

They said that to start a worker, use the postMesage().

First question: So if my main js file postMessage("Naruto"), why did the worker displayed first the two "WHERE'S SASUKE?" and then displayed Naruto and Sakura? Isnt it supposed to trigger its onMessage event first because it received a data from the main thread?

Second question: When I postMessage("Naruto"), it showed the two "WHERE'S SASUKE?". But why is that when I do postMessage("Sakura"), it didnt show the two "WHERE'S SASUKE?"? I mean, I called postMessage() in the main thread twice, why is that there's only two "WHERE'S SASUKE" displayed? Isnt it supposed to 'execute' the worker.js twice also thus seeing four "WHERE'S SASUKE?"? (Enlighten me please)

1/ "They said that to start a worker, use the postMesage()." says who ? You registered the main "thread" to the working activity ,it's all it takes to broadcast messages from the worker. 2/ look at from where you broadcast your messages from the main thread to the worker why would the worker respond "WHERE'S SASUKE" each time you send a message, since your script is not doing that ? — mpm
developer.mozilla.org/en-US/docs/DOM/Using_web_workers Spawning a worker section. Line 6 of code. I just used also the term, but you know the meaning — raberana
Except the exemple is not posting messages from the worker , which starts the worker thread too — mpm
Because you are posting messages from the worker , the worker doesnt have to wait a message from the main thread to start. it starts as soon as you post a message from either the worker or the main thread. The comment on Mozilla site just says that a post starts the worker activity , not a post "from the main thread only" — mpm
where's sasuke? .. sasuke is with Oruchimaru, trying to find the meaning of village and shinobi! Hashirama (by Impure World Reincarnation) is explaining him. — InfantPro'Aravind'

lostsource lostsource · Accepted Answer · 2013-01-19T08:40:16

Some annotations which may help you understand what's going on

main.js

var worker = new Worker("../Scripts/worker.js");

// register handler, 
// code is executed only when a message is received from worker
worker.onmessage = function (event) {
    alert("Worker said : " + event.data);
};

worker.js

// register onmessage handler , 
// code will not be executed at this point but only when you post a message
self.onmessage = function (event) {
      self.postMessage("Hi " + event.data);
};

// these are executed immediately
// they will be executed only once during the 'new Worker' part
self.postMessage("WHERE'S SASUKE? [1]");
self.postMessage("WHERE'S SASUKE? [2]");

HTML5 WebWorker Logic flow

1 Answers