when then JavaScript

when.js

var when = function(funcs){
    if(!(this instanceof when)){
        return new when(arguments);
    }
    this.funcs = Array.prototype.slice.call(funcs);
}
when.prototype.then = function(then){
   var i = 0,
       funcs = this.funcs,
       l = funcs.length,
       results = [],
       // Custom Object replaces func when pass is called
       complete = {},
       // insure all functions have successfully completed
       // before calling then function
       try_then = function(){
           var i=0;
           // insure all functions have run
           while(i<l){
               if(funcs[i++]!==complete)return;
           }
           then(results);
           // Prevent multiple calls to then
           then = function(){};
       }
   while(i<l)(function(i){
       var pass = function(result){
         results[i] = result
         funcs[i] = complete;
         try_then();
       }
       funcs[i](pass)
   })(i++);
};

when(
    function(pass){
       setTimeout(pass,3000);
    },
    function(pass){       
       pass('2nd');
    }
)
.then(function(results){
    console.log(results);
})