Javascript ES6 Promise Function Options

Question

I have an async function which can call one of multiple other async functions; I can split this up into multiple .then.catch chains, but I'm wondering if I can merge them together somehow. What I have is:

return new Promise((resolve, reject) => {
    if (payload.method === 'a')
        doFunctionA(arg)
        .then((x) => resolve())
        .catch((error) => reject())
    else if (payload.method === 'b')
        doFunctionB()
        .then((x) => resolve())
        .catch((error) => reject())
});

That's simplified, but is there another way to write this so that the then and catch is only written once? Like:

return new Promise((resolve, reject) => {
    var f = (payload.method === 'a' ? doFunctionA(arg) : doFunctionB());
    f()
    .then((x) => resolve())
    .catch((error) => reject())
});

Answer 1

Since doFunctionA and doFunctionB already return Promises, you don't have to wrap them in another Promise:

(payload.method === 'a' ? doFunctionA : doFunctionB)(arg)
  .then((x) => resolve())
  .catch((error) => reject())