CODEWITHSUNDEEP
javascriptloops
user2013286
user2013286

Reputation: 21

Creating javascript objects

Set UP: Hi. I am trying to learn about creating/instantiating objects. I was thinking I should be able to create multiple objects that may have different amounts of similar works (like gather news articles) and would "report completion" regardless of the order created. So far I am not clear on this, so here is a basic example followed by the stated question:

function test(count){
    this.count = count;
    for(var i = 0; i< count; i++){}
    console.log(i);
}

new test(1000);
new test(10);

Actual Question:

Based on the code above, I would expect the second instance to print first, but it does not. What would be the correct way to set this up so that which ever object finishes its work would print first?

* Modify my question * Sorry...what I am really intending to ask is how to set objects to have more of an asynchronous behavior. I am new to Stack, so please let me know if I should close/move this question.

Upvotes: 1

Views: 53

Answers (4)

Govind Balaji
Govind Balaji

Reputation: 639

The second instance gets instantiated only after first object is instantiated.
So it first prints 1000 after it comes to new test(10)
Because it is single threaded program

Upvotes: 1

Mathias Schwarz
Mathias Schwarz

Reputation: 7197

The reason why the second instance does not print first is that the first call new test(1000) runs to completion before the next line new test(10) starts executing.

If you want the second call to run first, swap the two lines...

Edit: By the way, any decent compiler will remove this line completely:

for(var i = 0; i< count; i++){}

So you can't even expect the first call to take more time than the second...

Upvotes: 1

Sirko
Sirko

Reputation: 74036

In general JavaScript is uses a synchronous execution model, the event queue. All calls are placed here, basically in the order they appear in your source code (respecting the scope they are in).

So if you start some function, nothing else is executed until that very function is finished. In your case you place both calls on the event queue, but the second call will only be executed, when the first one has finished.

There, however, exceptions: Worker or AJAX requests.

Here the execution is outside the usual event queue and you use message handlers or callbacks to use the results, after the execution is finished. In most cases, however, you can't be sure in which order the calls are finished as there are many circumstances affecting the ordering of execution (network delay, cpu usage, etc.)

In your case, it seems, you want to load external resources, anyway. So have a look at how AJAX works.

Upvotes: 1

Denys S&#233;guret
Denys S&#233;guret

Reputation: 382122

You're not creating different parallel execution threads : the first test(1000) is wholly executed before the following line even starts.

In Javascript, when you're not using webworkers (which you should probably not use), all your code is always executed in a single thread. This thread is awaken by the browser on events and goes back to sleep when the function called by the browser returns.

Note that even with threads, even in naturally parallel languages, you hardly would have had any guarantee regarding what loop ends first.

Upvotes: 1

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