Basic JS Deferred object implementation

gistfile1.js

/* 
** Solution proposed by: Chad Elliott (https://www.vizify.com/thethechad)
** at StackOverflow. Link to original: http://stackoverflow.com/a/18097040
*/

function Deferred(){
  this._done = [];
  this._fail = [];
}
Deferred.prototype = {
  execute: function(list, args){
    var i = list.length;

    // convert arguments to an array
    // so they can be sent to the
    // callbacks via the apply method
    args = Array.prototype.slice.call(args);

    while(i--) list[i].apply(null, args);
  },
  resolve: function(){
    this.execute(this._done, arguments);
  },
  reject: function(){
    this.execute(this._fail, arguments);
  }, 
  done: function(callback){
    this._done.push(callback);
  },
  fail: function(callback){
    this._fail.push(callback);
  }  
}


/*
** Usage example
*/

var v;

var setVal = function() {
    var d = new Deferred();
    setTimeout(function() {
        v = 'a value';
        d.resolve(this);
    }, 5000);
    return d;
};

setVal().done(function() {
    console.log('all done :' + v);
});