How to migrate from Q.js?

I’m currently using Q.js and investigating bluebird. Would be nice if i could just replace var q=require("Q") With q=require("bluebird")

What should I expect?

[petkaantonov]

I finally got around it

https://github.com/petkaantonov/bluebird-q https://www.npmjs.com/package/bluebird-q

@spion Unfortunately bbq was taken 😛

[petkaantonov]

@xaka

In short:

Bluebird is 2 orders of magnitude (~100x) faster with more features and with the shared features being better, for example full stack traces. It also uses 20x less memory. Memory usage and performance alone is reason enough if you are using promises at server side.

Personally the feature to die for is promisifyAll which in many cases turns a callback api into optimized promise api. Ironically this will give you more performance than libraries that use promises to begin with (due to cast overhead). Although if those other libraries use bluebird and you use bluebird 1.0.2, casting will be very fast again.

For example with the redis library:

var Promise = require("bluebird");
Promise.promisifyAll(require("redis").RedisClient.prototype);

...

redisClient.getAsync("key").then(...)

(The redis api will have *Async methods that return bluebird promises with just 1 line)

There is many intricacies with this, for example the promisified methods allow you to differentiate between thrown errors and callback errors using the .catch(RejectionError) or .error (also unique bluebird feature) which many people have needed.

Features that have no correspondence in Q:

• promisifyAll
• predicate and error type extension for .catch
• .bind
• cancellation
• .map
• .reduce
• .filter
• .props
• .any
• .some