altCognito altCognito - 1 year ago 194
Javascript Question

Bookmarklet wait until Javascript is loaded

I've got a bookmarklet which loads jQuery and some other js libraries.

How do I:

  • Wait until the javascript library I'm using is available/loaded. If I try to use the script before it has finished loading, like using the $ function with jQuery before it's loaded, an undefined exception is thrown.

  • Insure that the bookmarklet I load won't be cached (without using a server header, or obviously, being that this is a javascript file: a metatag)

Is anyone aware if onload for dynamically added javascript works in IE? (to contradict this post)

What's the simplest solution, cleanest resolution to these issues?

Answer Source

It depends on how you are actually loading jQuery. If you are appending a script element to the page, you can use the same technique that jQuery uses to dynamically load a script.

EDIT: I did my homework and actually extracted a loadScript function from the jQuery code to use in your bookmarklet. It might actually be useful to many (including me).

function loadScript(url, callback)
    var head = document.getElementsByTagName("head")[0];
    var script = document.createElement("script");
    script.src = url;

    // Attach handlers for all browsers
    var done = false;
    script.onload = script.onreadystatechange = function()
        if( !done && ( !this.readyState 
                    || this.readyState == "loaded" 
                    || this.readyState == "complete") )
            done = true;

            // Continue your code

            // Handle memory leak in IE
            script.onload = script.onreadystatechange = null;
            head.removeChild( script );


// Usage: 
// This code loads jQuery and executes some code when jQuery is loaded
loadScript("", function()
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