Javascript: asynchronous function-calls using jQuery

Question

I am currently experimenting with asynchronous function-calls in jQuery and am stuck. Consider the following example:

<html>
    <head>
        <script type="text/javascript" src="http://code.jquery.com/jquery-1.7.2.min.js"></script>
    </head>
    <body>
        <script type="text/javascript">
            f = function() {
                alert("f1");
                var x = 0;
                for (var i = 0; i < 2500000000; i++) {
                    x++;
                }
                alert("f2");
            }

            $.when( f() ).done(alert("done"));
            alert("moving on...");
        </script>
    </body>
</html>

I would expect the alert-messages in the following order: "f1", "moving on...", "f2", "done" But when I run the code in Chrome, what I get is this: "f1", nothing happens for 10s, "f2", "done", "moving on...". This doesn't look asynchronous to me. Am I doing something wrong or is this the intended behavior? If so, what is the whole point of using the when-function and the callback? Couldn't I just call the function f synchronously?

api.jquery.com/jQuery.when

SLaks
– SLaks

2012-06-17 14:52:35 +00:00
Commented Jun 17, 2012 at 14:52 — SLaks
– SLaks, Commented Jun 17, 2012 at 14:52

SLaks · Accepted Answer · 2012-06-17 14:51:15Z

2

 $.when(f())

This calls f() immediately (like any other function call), then passes the result to $.when.

$.when() does not magically make a function asynchronous; it can only work with existing asynchronous operations (eg, AJAX).

The only way to do actual multi-threading in Javascript is to use Web Workers.

answered Jun 17, 2012 at 14:51

SLaks

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Comments

Ajay Singh Beniwal · Accepted Answer · 2012-06-17 15:22:26Z

0

$.when takes a deffered value or a normal value . If normal value is passed it is called immediately and if deffered value is passed it is called at the time of operation completion For is not a async operation in javascript so it is executed immediately.Refer to below example for normal value passed inside when

 $.when({ x: 10 }).then(function (option) {
            alert(option.x);
        })

answered Jun 17, 2012 at 15:22

Ajay Singh Beniwal

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