A robust remote JS dependency manager

require.js

var require =  (function(){
  var requires = {};

  return function(filename, callback){
    if(typeof(requires[filename]) === "undefined"){
      requires[filename] = {
        callbacks: [],
        state: "initializing",
      };
    }

    var state = requires[filename].state;

    if(callback){
      if(state === "done"){
        callback();
        return;
      } else {
        if(callback) requires[filename].callbacks.push(callback);
      }
    }

    if(state === "initializing"){
      requires[filename].state = "fetching";

      $.getScript(filename, function(){
        requires[filename].state = "done";
        $.each(requires[filename].callbacks, function(){
          this();
        });
      });
    }

  };
})(),
// require("http://example.com/foo.js");
// require("http://example.com/foo.js", function(){alert("loaded!")});
// // User will see "loaded!" once. Allows you to pre-load the JS a rest assured that the callback will be called exactly once