Bookmarklet wait until Javascript is loaded

Question

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 1

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
            callback();

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

    head.appendChild(script);
}


// Usage: 
// This code loads jQuery and executes some code when jQuery is loaded
loadScript("https://code.jquery.com/jquery-latest.js", function()
{
    $('my_element').hide();
});

Answer 2

To answer your first question: Javascript is interpreted sequentially, so any following bookmarklet code will not execute until the library is loaded (assuming the library was interpreted successfully - no syntax errors).

To prevent the files from being cached, you can append a meaningless query string...

url = 'jquery.js?x=' + new Date().getTime();

Answer 3

I've paid an attention that in Chrome the order of scripts that are loaded is undetermined, when using @Vincent Robert's technique. In this case a little modification helps:

(function() {
    var callback = function() {
        // Do you work
    };
        // check for our library existence
    if (typeof (MyLib) == 'undefined') {
        var sources = [
                'http://ajax.cdnjs.com/ajax/libs/json2/20110223/json2.js',
            'https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js',
            'https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.13/jquery-ui.min.js',
            'http://myhost.com/javascripts/mylib.min.js'];

        var loadNextScript = function() {
            if (sources.length > 0) {
                var script = document.createElement('script');
                script.src = sources.shift();
                document.body.appendChild(script);

                var done = false;
                script.onload = script.onreadystatechange = function() {
                    if (!done
                            && (!this.readyState || this.readyState == "loaded" || this.readyState == "complete")) {
                        done = true;

                        // Handle memory leak in IE
                        script.onload = script.onreadystatechange = null;

                        loadNextScript();
                    }
                }
            } else {
                callback();
            }
        }
        loadNextScript();

    } else {
        callback();
    }
})();

Answer 4

I got a little closer with this, but not completely. It would be nice to have a discrete, example of a bookmarklet that demonstrated how to avoided caching.