var Loader = function () { }
Loader.prototype = {
 require: function (scripts, callback) {
  this.loadCount  = 0;
  this.totalRequired = scripts.length;
  this.callback  = callback;
  for (var i = 0; i < scripts.length; i++) {
   this.writeScript(scripts[i]);
  }
 },
 loaded: function (evt) {
  this.loadCount++;
  if (this.loadCount == this.totalRequired && typeof this.callback == 'function') this.callback.call();
 },
 writeScript: function (src) {
  var self = this;
  var s = document.createElement('script');
  s.type = "text/javascript";
  s.async = true;
  s.src = src;
  s.addEventListener('load', function (e) { self.loaded(e); }, false);
  var head = document.getElementsByTagName('head')[0];
  head.appendChild(s);
 }
}

var l = new Loader();
l.require([
 "example-script-1.js",
 "example-script-2.js"],
 function() {
  // Callback
  console.log('All Scripts Loaded');
 });