Never Mix Promises and Callbacks in NodeJS

Re:Never Mix Promises and Callbacks in NodeJS by ascagnel_ on Friday April 07, 2017 @12:24PM (#14061054)

If you must call the callback, you could simplify this pattern as such:

  function fetchFirstUser(isWhatIWant, callback) {
      knex.first().from('users')
          .then(user => ({ user }))
          .catch(e => ({ e }))
          .then(({ user, e }) => {
              if (user) {
                  callback(user);
              } else {
                  callback(e);
              }
          });
  }

By only calling your callback function after a catch statement, you guarantee that (a) an exception generated by the callback will not be swallowed by the catch statement and that (b) the callback is called exactly once in the promise chain.

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Re:Never Mix Promises and Callbacks in NodeJS by spankalee on Friday April 07, 2017 @12:55PM (#14061354)

I like this!

For golfing purposes, you can remove a branch too:

    function fetchFirstUser(isWhatIWant, callback) {
      knex.first().from('users')
        .then((user) => ({ user }), (e) => ({ e }))
        .then(({ user, e }) => callback(e, user))
        .catch((e) => console.error(e));
    }

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Re:Never Mix Promises and Callbacks in NodeJS by Vevolut on Friday April 07, 2017 @12:53PM (#14061343)

I may be mistaken but I don't think this will work exactly how you expect it to. If theres an unhandled exception thrown somewhere in the callback then it will fail silently. You need to add a .catch(console.error.bind(console)); at the very end to get back to default behavior.

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