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Asked: 2026-06-13T23:04:06+00:00

Here is the circumstance: I have 2 pages: 1 x html page 1 x

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Here is the circumstance:
I have 2 pages:

  • 1 x html page
  • 1 x external Javascript

Now in the html page, there will be internal Javascript coding to allow the placement of the window.onload, and other page specific methods/functions.

But, in the external Javascript I want certain things to be done before the window.onload event is triggered. This is to allow customized components to be initialized first.

Is there a way to ensure initialization to occur in the external Javascript before the window.onload event is triggered?

The reason I have asked this, is to attempt to make reusable code (build once – use all over), to which the external script must check that it is in ‘order/check’ before the Javascript in the main html/jsp/asp/PHP page takes over. And also I am not looking for a solution in jQuery @_@

Here are some of the links on Stack Overflow I have browsed through for a solution:

Can someone help or direct me to a solution, your help will be muchness of greatness appreciated.

[updated response – 19 November 2012]

Hi all, thanks for you advice and suggested solutions, they have all been useful in the search and testing for a viable solution.
Though I feel that I am not 100% satisfied with my own results, I know your advice and help has moved me closer to a solution, and may indeed aid others in a similar situation.

Here is what I have come up with:

test_page.html

<html>
<head>
<title></title>
<script type="text/javascript" src="loader.js"></script>
<script type="text/javascript" src="test_script_1.js"></script>
<script type="text/javascript" src="test_script_2.js"></script>
<script type="text/javascript">
window.onload = function() {
    document.getElementById("div_1").innerHTML = "window.onload complete!";
}
</script>

<style type="text/css">
div {
    border:thin solid #000000;
    width:500px;
}
</head>
<body>
    <div id="div_1"></div>

    <br/><br/>

    <div id="div_2"></div>

    <br/><br/>

    <div id="div_3"></div>
</body>
</html>

loader.js

var Loader = {
    methods_arr : [],

    init_Loader : new function() {
        document.onreadystatechange = function(e) {
            if (document.readyState == "complete") {
                for (var i = 0; i < Loader.methods_arr.length; i++) {
                    Loader.method_arr[i]();
                }
            }
        }
    },

    load : function(method) {
        Loader.methods_arr.push(method);
    }
}

test_script_1.js

Loader.load(function(){initTestScript1();});

function initTestScript1() {
    document.getElementById("div_1").innerHTML = "Test Script 1 Initialized!";
}

test_script_2.js

Loader.load(function(){initTestScript2();});

function initTestScript2() {
    document.getElementById("div_2").innerHTML = "Test Script 2 Initialized!";
}

This will ensure that scripts are invoked before invocation of the window.onload event handler, but also ensuring that the document is rendered first.

What do you think of this possible solution?

Thanking you all again for the aid and help 😀

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1 Answer

  1. Editorial Team

    Basically, you’re looking for this:

    document.onreadystatechange = function(e)
{
    if (document.readyState === 'complete')
    {
        //dom is ready, window.onload fires later
    }
};
window.onload = function(e)
{
    //document.readyState will be complete, it's one of the requirements for the window.onload event to be fired
    //do stuff for when everything is loaded
};

    see MDN for more details.

    Do keep in mind that the DOM might be loaded here, but that doesn’t mean that the external js file has been loaded, so you might not have access to all the functions/objects that are defined in that script. If you want to check for that, you’ll have to use window.onload, to ensure that all external resources have been loaded, too.

    So, basically, in your external script, you’ll be needing 2 event handlers: one for the readystatechange, which does what you need to be done on DOMready, and a window.onload, which will, by definition, be fired after the document is ready. (this checks if the page is fully loaded).
    Just so you know, in IE<9 window.onload causes a memory leak (because the DOM and the JScript engine are two separate entities, the window object never gets unloaded fully, and the listener isn’t GC’ed). There is a way to fix this, which I’ve posted here, it’s quite verbose, though, but just so you know…

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