Working with promises inside an if/else

Question

I have a conditional statement in which I need to perform one of two operations, then continue after whichever operation has resolved. So my code currently looks as follows:

Answer 1

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)

Answer 2

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
}

Answer 3

more_code = miFunc() => return new Promise((resolve, reject) => ... });

Solution 1

const waitFor = should_do_thing_a ? do_thing_a() : do_thing_b();
waitFor.then(...).catch(...)

Solution 2

let waitFor = Promise.resolve();

if (do_thing_a) {
    waitFor = do_thing_a();
} else {
    waitFor = do_thing_b();
}

waitFor.then(...).catch(...);

Answer 4

Save the promise and add the then after the if statement:

var promise;

if (shoud_do_thing_a) {
  promise = do_thing_a();
} else {
  promise = do_thing_b();
}

promise.then(more_code);

Answer 5

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)

Answer 6

var promise = shoud_do_thing_a? do_thing_a: do_thing_b

promise().then(function () {
// more code    
})