When-Then (pseudo javascript Promise)

whenthen.js

var when = function(){
    if( !(this instanceof when) ) return new when(arguments); //return new instance of itself

    var self = this; //cached so the syntax of code within the function is more readable

    self.pending = Array.prototype.slice.call(arguments[0]); //convert arguments passed in to array
    self.pending_length = self.pending.length; //cache length of the arguments array
    self.results = []; //container for results of async functions

    (function(){ // define pass() within this context so that the outer scope of self(this) is available when pass() is executed within the user's async functions
        self.pass = function(){

            self.results.push(arguments); //push async results to cache array
            
            if( self.results.length === self.pending_length ) //if all async functions have finished, pass the results to .then(), which has been redefined to the user's completion function
                self.then.call(self, self.results); 
        };
    })();
}
when.prototype = {
    then: function(){
        
        this.then = arguments[0]; //reassign .then() to the user-defined function that is executed on completion. Also ensures that this() can only be called once per usage of when()
        
        while(this.pending[0]){
            this.pending.shift().call(this, this.pass); //execute all functions user passed into when()
        }

    }
}



//#### TEST CASE 1 ####
when(
    function(pass){
        pass(2);
    },
    function(pass){

        setTimeout(function(){
            pass(1000);
        }, 1000);

    },
    function(){
        
        setTimeout(function(){
            pass(100);
        }, 100);

    },
    function(){
        
        setTimeout(function(){
            pass(2000);
        }, 2000);

    }
)
.then(function(results){
    console.log(results);
})



//#### TEST CASE 2 (Node.js required) ####
var http = require('http');

var get = function(url, pass){
    http.get({ host: url, port: 80 }, function(res){
        var body = [];
        res.on('data', function(chunk){
            body.push(chunk);
        })
        .on('end', function(){
            
            pass(body.join(''));
            
        });
    })
    .on('error', function(err){
        pass(err);
    });
}

when( 
    function(pass){
        get('www.google.com', pass);
    },
    function(pass){
        get('news.ycombinator.com', pass);
    },
    function(pass){
        get('io9.com', pass);
    }
)
.then(function(results){

    console.log(results);

});

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