Sample script to load a script asynchronously whilst queuing method calls. Inspired by the Google Analytics tracking code.

html.js

// Placed into HTML
(function(window, document, tag, src, property, script, before)
{
    window['LoaderObject'] = property;

    window[property] = window[property] || function()
    {
        (window[property].q = window[property].q || []).push(arguments);
    }

    script = document.createElement(tag);
    script.async = 1;
    script.src = src;

    document.getElementsByTagName(tag)[0].parentNode.insertBefore(script, before);
}(window, document, 'script', '/path/to/loader.js', 'loader'));


// Queue instance method
loader('someMethod', 'string', 1234);

loader.js

(function(window, document)
{
    var property = window['LoaderObject'],
        loader = window[property],
        params;

    loader.someMethod = function(str, num)
    {
        console.log('someMethod called', str, num);
    };

    for (var i in loader.q || [])
    {
        params = Array.prototype.slice.call(loader.q[i]);
        loader[params.shift()].apply(loader, params);
    }
}(window, document));