Mastering JavaScript Promises

Q.Promise() – another way to create promises

Q.Promise is an alternative promise-creation API that has the same power as the deferred concept, but without introducing another conceptual entity.

Let's rewrite the preceding requestOkText example using Q.Promise:

function requestOkText(url) { return Q.Promise(function(resolve, reject, notify) { var request = new XMLHttpRequest(); request.open("GET", url, true); request.onload = onload; request.onerror = onerror; request.onprogress = onprogress; request.send(); function onload() { if (request.status === 200) { resolve(request.responseText); } else { reject(new Error("Status code was " + request.status)); } } function onerror() { reject(new Error("Can't XHR " + JSON.stringify(url))); } function onprogress(event) ...