Simple JS Deferred/Promise implementation

gistfile1.js

// promise definition
var Promise = function() {
    this.successCallbacks = [];
    this.errorCallbacks = [];
};

Promise.prototype.then = function(successCallback, errorCallback) {
    console.log('then()');

    this.successCallbacks.push(successCallback);

    if (errorCallback) {
        this.errorCallbacks.push(errorCallback);
    }
};

// defer definition
var Defer = function () {
    this.promise = new Promise();
};

Defer.prototype.resolve = function(data) {
    console.log('resolve()');

    this.promise.successCallbacks.forEach(function(callback) {
        window.setTimeout(function () {
            console.log(callback);

            callback(data);
        }, 0);
    });
};

Defer.prototype.reject = function(error) {
    console.log('reject()');

    this.promise.errorCallbacks.forEach(function(callback) {
        window.setTimeout(function () {
            console.log(callback);

            callback(error);
        }, 0);
    });
};