Working with promises inside an if/else

If you can use async/await

async function someFunc() {
    var more_code = function () { 
        // more code
    }

    if (shoud_do_thing_a) {
        await do_thing_a()
    } else {
        await do_thing_b()
    }

    more_code()
}

Or if you can't, use then():

var more_code = function () { 
    // more code
}

var do_thing;
if (shoud_do_thing_a) {
  do_thing = do_thing_a()
} else {
  do_thing = do_thing_b()
}

do_thing.then(more_code)

If you're stuck with raw Promises and can't use async/await (You usually should have no trouble, what with babel/typescript etc), the following is a bit more elegant than storing the promise in a variable:

function something() {
  return Promise.resolve()
    .then(() => {
      if (should_do_thing_a) {
        return do_thing_a();
      }
      else if (should_do_thing_b) {
        return do_thing_b();
      }
    })
    .then(some_more_code);
}

Note that when you start working with Promises, your functions should always return a Promise that other functions can work with. Leaving an asynchronous action without any way to handle it means bad things, especially when it comes to error handling.

In a more general sense, it means that when you use Promises, more of your code is "uplifted" into being executed and returned as Promises.

How I want to improve on other answers:

• keep it clean and simple
• no unneeded variables
• return promise asap
• in js we use camelCase
• put it in a function and name that function to keep it readable
• let then execute moreCode so it's called after the thing is done.

---

function doTheThing () {
  if (shouldDoA) return doThingA()
  else return doThingB()
}

doTheThing().then(moreCode)

Simple working example:

The scope it's defined in must be async.

const createUser = async (data) => {
   if (await isUsernameTaken(username)) { return 'username-taken' }
}

The isUsernameTaken func:

const isUsernameTaken = async (username) => {
    const request = await API.SomeRequest
    return !request.isEmpty
}