Promise

سینتکس جدید promise در جاواسکریپت:

لینک و MDN

function httpGet(url) {
        return new Promise(
            function (resolve, reject) {
                var request = new XMLHttpRequest();
                request.onreadystatechange = function () {
                    if (this.status === 200) {
                        // Success
                        resolve(this.response);
                    } else {
                        // Something went wrong (404 etc.)
                        reject(new Error(this.statusText));
                    }
                }
                request.onerror = function () {
                    reject(new Error(
                        'XMLHttpRequest Error: '+this.statusText));
                };
                request.open('GET', url);
                request.send();    
            });
    }