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Editorial Team
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Asked: 2026-05-27T18:52:39+00:00

We use a bit of javascript that overwrites the setTimeout method for IE. This

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We use a bit of javascript that overwrites the setTimeout method for IE. This is because in some versions of IE the parameters do not get passed correctly (see here).

I have to load the modified setTimeout script first, because if I load it after the code that calls setTimeout is parsed (not run) then the modifed version does not get called.

What happens when the javascript engine parses files that have method calls to methods at the global scope? Do the mappings to the methods get created at parse time or when the code is executed?

EDIT

I have had a few answers to this question, which give other solutions to this problem, but the problem at hand is not my concern as I already have a solution for it. What I want to gain by this question is a better understanding of how javascript is parsed and run.

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1 Answer

  1. Editorial Team

    EDIT #2

    Fiddle #1 – http://jsfiddle.net/zEaL8/4/ – Allows you to set/reset a native function. To see how the redefinition and calling order works.

    Fiddle #2 – http://jsfiddle.net/aKnjA/1/ -Demonstrates that the order of definition does not matter. Notice that the redefinition happens after the browser parses the call to the function.

    EDIT

    To answer your question: Javascript does not enforce any order of definition of functions. i.e. we can call a function defined afterwards in code. When the browser parses a line of code that calls a function that is defined afterwards, it does not have any clue as to where to find that function. This being the case, it is clear that binding happens only at run-time and not during initial parse. This in effect would mean that your redefinition of setTimeout is what will execute. The only thing to ensure is that the redefinition of setTimeout itself gets executed before any call to that is executed.

    To ensure that the redefinition of your new setTimeout is processed first, you can place it in a script block as the first element inside the head node outside load, domReady etc.

    i.e. Something like:

    <html>
<head>
<script>
window.setTimeout = function() {
    alert('new sT');
}
</script>
</head>
<body onload="setTimeout();"></body>
</html>
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