Understanding promises in Node.js

javascript node.js promise
ajsie picture ajsie · Nov 28, 2010 · Viewed 98.2k times · Source

From what I have understood there are three ways of calling asynchronous code:

  1. Events, e.g. request.on("event", callback);
  2. Callbacks, e.g. fs.open(path, flags, mode, callback);
  3. Promises

I found the node-promise library but I don’t get it.

Could someone explain what promises are all about and why I should use it?

Also, why was it removed from Node.js?

Answer

enyo picture enyo · May 16, 2012

Since this question still has many views (like mine) I wanted to point out that:

  1. node-promise looks rather dead to me (last commit was about 1 year ago) and contains nearly no tests.
  2. The futures module looks very bloated to me and is badly documented (and I think that the naming conventions are just bad)
  3. The best way to go seems to be the q framework, which is both active and well-documented.

Related questions

Using async/await with a forEach loop

Are there any issues with using async/await in a forEach loop? I'm trying to loop through an array of files and await on the contents of each file. import fs from 'fs-promise' async function printFiles () { const files = await getFilePaths() // …

Read More
Getting a UnhandledPromiseRejectionWarning when testing using mocha/chai

So, I'm testing a component that relies on an event-emitter. To do so I came up with a solution using Promises with Mocha+Chai: it('should transition with the correct event', (done) => { const cFSM = new CharacterFSM({}, emitter, transitions); let …

Read More
Why is my asynchronous function returning Promise { <pending> } instead of a value?

My code: let AuthUser = data => { return google.login(data.username, data.password).then(token => { return token } ) } And when i try to run something like this: let userToken = AuthUser(data) console.log(userToken) I'm getting: Promise { <pending> } …

Read More