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

``` javascript
return doSomething(foo).then(function(result) {
// ...
}).then(function(result2) {
// ...
}).then(function(result3) {
// ...
}).catch(function(error) {
// ...
}).finally(function() {
// ...
});
```
#### Option 2: named functions

``` javascript
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?

Start by reading the existing guide and its promise-related sections, then review this issue's discussion about anonymous versus named functions. Done means the project reaches a documented decision and the guide contains the agreed readability guidance.

Written by the indexing model from the issue text.