A Custom Promise

promise.js

var Promise = function(){
    this.pending = [];
}

Promise.prototype = {
    then: function(onResolve, onReject){

        this.pending.push({ 
            resolve: onResolve, 
            reject: onReject 
        })

        return this
    },

    resolve: function(data){
        this.then = function(reject, resolve){ 
            resolve && resolve(data) 
        }

        this.executePending('resolve', data)
    },

    reject: function(data){
        this.then = function(reject, resolve){ 
            reject && reject(data) 
        }

        this.executePending('reject', data)
    },

    executePending: function(type, data){
        var p, i = 0
        while (p = this.pending[i++]) { 
            p[type] && p[type](data) 
        }

        delete this.pending
    }
}