this.then = function (onFulfilled,onRejected) {
    return new Promise(function (resolve, reject) {
        switch (state){
            case "pending":
                callbacks.push([
                    function () {
                        resolve(onFulfilled(result));
                    },
                    function () {
                        reject(onRejected(result));
                    }
                ]);
                break;
            case "fulfilled":
                resolve(onFulfilled(result));
                break;
            case "rejected":
                reject(onRejected(result));
                break;
        }
    });
};