Add a file to the page.

addFile.js

function addScript(type,url,cache,cb){
  var script = document.createElement(type),
    head=document.getElementsByTagName('head')[0],
    done=false,
    src = url;
    src += (cache === false)?('?dummy=' + (+new Date())):'';

  script.onload=script.onreadystatechange = function(){
    if ( !done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete') ) {
      done=true;
      if(typeof cb === 'function') cb();
      script.onload = script.onreadystatechange = null;
      head.removeChild(script);
    }
  };
  script.src = script.href = src;
  head.appendChild(script);
}