Ask HN: Is JavaScript abandoning Promises

2 points by bengg 8 years ago | 4 comments

Recently in a technical screening, a senior engineer asked me what I thought about Javascript moving away from Promises in favor of Observables. I replied that I didn't know that Javascript was moving away from Promises, since Promises are part of the ES6 spec.

In general, I was blindsided by this. So my 2 questions are:

1. Is Javascript truly moving away from Promises in favor of Observables?

2. Where can I read about the direction that Javascript is taking, so that I can have an educated discussion on the future of Javascript?

WorldMaker 8 years ago |

Promises aren't going anywhere. async/await is built on top of Promises, for instance.

Observables are in position to be adopted by ECMAScript in a future spec eventually, but they are still only at Stage 1 of the ES proposal process, and also Observables don't exactly replace Promises so much as extend them.

An Observable can be thought of as a "stream" of promised values rather than just a single promised value. It's a somewhat different paradigm. From the Observable perspective a Promise is a simple Observable that produces a single value and completes immediately after. So you can see Promises are useful in an Observable world as something of a building block.

A good resource on Observables can be: http://reactivex.io/

It's focused on the main cross-platform library for Observables (ReactiveX which has implementations in .NET, Java, JS, more), but a lot of it is applicable to Observables in general and it has a lot of good "marble" diagrams that can help show why Observables can be powerful.

The dry Stage 1 ES spec itself is here: https://github.com/tc39/proposal-observable

justsml 8 years ago |

Promises are one of those features misunderstood for 2 reasons. Several leading initial library implementations were broken from day 1, and couldn't/wouldn't later introduce breaking changes to existing users.

Another factor dragging down the impression of Promises: Google search seems to love returning 5+ year old articles. They almost universally suck. Even the stuff I wrote back then was awful.

New articles are not necessarily spared, they often suffer from a number of issues: Overly Simplistic examples, fragile function boundaries, leaky variables, arbitrary 'design.'

I just updated my write-up on avoiding Promise anti-patterns: https://github.com/justsml/escape-from-callback-mountain/wik...

The main project's README shows how to rock modern Promises: https://github.com/justsml/escape-from-callback-mountain/

ahookom 8 years ago |

I keep hearing about async/await being a cleaner way to write asynchronous code in JavaScript but async/await actually makes use of promises in the implementation. That's what I would have talked about. For more: https://hackernoon.com/6-reasons-why-javascripts-async-await...

borplk 8 years ago |

Promises are not going anywhere.