Dynamic, cross-browser script loading - from head.js lib

gistfile1.js

// From the headjs code:

function scriptTag(src, callback) {

    var s = doc.createElement('script');
    s.type = 'text/' + (src.type || 'javascript');
    s.src = src.src || src;
    s.async = false;

    s.onreadystatechange = s.onload = function() {

        var state = s.readyState;

        if (!callback.done && (!state || /loaded|complete/.test(state))) {
            callback.done = true;
            callback();
        }
    };

    // use body if available. more safe in IE
    (doc.body || head).appendChild(s);
}