Load JavaScript Dynamically and Invoke something onLoad

load.js

function require(file,callback){
    var head=document.getElementsByTagName("head")[0];
    var script=document.createElement('script');
    script.src=file;
    script.type='text/javascript';
    //real browsers
    script.onload=callback;
    //Internet explorer
    script.onreadystatechange = function() {
        if (_this.readyState == 'complete') {
            callback();
        }
    }
    head.appendChild(script);
}