Q Promise Equivalent of BlueBird Promise.Bind()

Question

Q Promise Equivalent of BlueBird Promise.Bind()

Few questions, does Q have a bind() method as seen in BlueBird API and this slide JavaScript Promises ~Kerrick Long? Is it part of the Core Promise/A+ Spec? If not, is there a polyfill or workaround for it?

javascript
node.js
promise
q
bluebird

Answer 1

Well, the Promises/A+ spec only specifies how .then works, so .bind is not a part of the Promises/A+ spec. In fact Promises/A+ specifies that the this value behaves like a normal function call and promises are not bound - Bluebird gets around this limitation by returning a BoundPromise which is not a regular promise and interops seamlessly with other promise libraries.

There is no equivalent Q feature, once ES6 lands you'll be able to use the "fat arrow" => in order to lexically bind the scope in then chains:

this.x = 15;
Q().then(() => console.log(this.x)) // always logs 15

Generally speaking, this is one of many features Bluebird has over Q, there is no obvious way to 'shim it in' since it changes the behavior of .then - you'd have to override .then in Q promises and effectively create a wrapper over the whole library to accomplish that.