Simple promise implementation for Node.js and the browser

promise.js

(function() {
    
    if (typeof module !== 'undefined' && module.exports) {
        module.exports = Promise;
    } else {
        this.Promise = Promise;
    }
    
    function Promise(context) {
        this.context = context || this;
        this.callbacks = [];
        this.resolved = undefined;
    };

    Promise.prototype.then = function(callback) {
        if (this.resolved) {
            callback.apply(this.context, this.resolved);
        } else {
            this.callbacks.push(callback);
        }
    };

    Promise.prototype.resolve = function() {
        if (this.resolved) throw new Error('Promise already resolved');

        var callback;
        this.resolved = arguments;

        while (callback = this.callbacks.shift()) {
            callback.apply(this.context, this.resolved);
        }
    };
    
})();