Can I omit this catch block for this promise arrangement?

I'm trying to use best practice. And per my understanding you only need a catch clause at the end of a promise chain.

However this is not a straight forward chain. createUser() is in a then method. However should not any errors in createUser() be caught in getOrCreateUser()?

Can I omit the catch clause in createUser()?

function getOrCreateUser (accessToken, refreshToken, profile, done) {
  const user_props = obtainUserPropsFromGoogle(profile);
  DBM.getUser(user_props.id_google).then( (res) => {
    return res[0] ? done(null, user_props) : createUser(done, user_props);
  }).catch( error => {
    return done(error, null);
  });
}

function createUser (done, user_props) {
  DBM.createUser(user_props).then(() => {
    return done(null, user_props);
  }).catch( error => {
    return done(error, null);
  });
}

> Can I omit the catch clause in createUser()?

No, not the way the code is written.

In order to remove the catch from the inner promise, the outer promise needs to handle the rejection of the inner promise.

For that to happen, you need to return the inner promise from createUser. Then, you need to return that promise from the then handler on the outer promise.

You effectively have this:

Promise.resolve.then(() => {
  Promise.reject()
}).catch(/* cannot handle Promise.reject above */)

What you need is this:

Promise.resolve.then(() => {
  return Promise.reject();
}).catch(/* correctly handles above Promise.reject */)

In practical terms, your code should look like this:

function getOrCreateUser (accessToken, refreshToken, profile, done) {
  const user_props = obtainUserPropsFromGoogle(profile);
  DBM.getUser(user_props.id_google).then( (res) => {
    // Now that `createUser` returns its promise, this `return` is actually useful
    return res[0] ? done(null, user_props) : createUser(done, user_props);
  }).catch( error => {
    done(error, null);
  });
}

function createUser (done, user_props) {
  // This promise must be returned out of `createUser`
  return DBM.createUser(user_props).then(() => {
    done(null, user_props);
  })
}