Best practices for promises?

First of all, great job on this guide, I agree with it almost 100%. All of this should really be common knowledge, but I sure as hell didn’t know most of these things when I started, so kudos for writing it all down.

Now, since promises have been standardized and a lot of people have started using them, it would be nice to have a section on how to keep promise-based code readable. For instance, when chaining multiple promises together, there are at least two alternative ways to do it:

Option 1: anonymous functions

return doSomething(foo).then(function(result) {
  // ...
}).then(function(result2) {
  // ...
}).then(function(result3) {
  // ...
}).catch(function(error) {
  // ...
}).finally(function() {
  // ...
});

Option 2: named functions

function doThis(result) {
  // ...
}
function doThat(result) {
  // ...
}
function handleError(error) {
  // ...
}
function done() {
  // ...
}

return doSomething(foo)
  .then(doThis)
  .then(doThat)
  .catch(handleError)
  .finally(done);

The second way, while being somewhat more verbose, seems to be preferable, as the chain of tasks that the promise result travels through becomes more obvious.

I did an internal poll of our developers, and so far, option 2 seems to be ahead, although I have not heard from everyone yet. How does AirBnB deal with this, and what are your opinions?

[getvega]

About best practices, seems like you all put the .then on the same line instead of a new line…

What do you think of

getPromise()
    .then(function(response) {
         return response.body;
    })
    .then(function(body) {
         return body.user;
    });

It seems a bit more compliant with leading dots in https://github.com/airbnb/javascript#whitespace

[chandanch]

Chaining promises is fine but the chain should not go beyond 2 max. 3