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Editorial Team
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Asked: 2026-06-05T22:14:38+00:00

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

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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?

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1 Answer

  1. Editorial Team
     $.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.

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