Ways to add javascript files dynamically in a page

Question

I have seen Scriptaculous.js file to include its required javascript files dynamically. Is there any better approach to include javascript dynamically.

For example,

Answer 1

We can quickly extend this so that a callback can be performed once the script is added.

function loadjscssfile(filename, filetype, callback){
    if (typeof fileref!="undefined") {
        document.getElementsByTagName("head")[0].appendChild(fileref);
        callback();
    }
}