promisify resolves only single parametar

[snovakovic]

const fun = promisify((cb) => cb(undefined, 'res1', 'res2', 'res3'));

fun().then((r1, r2, r3) => {
  // r1 => 'res1'
  // r2 && r3 are undefined
});

[snovakovic]

resolve() can return only single value. To resolve this we could return array when there is multiple parameters.

fun().then(([r1, r2, r3]) => {
  // r1 => 'res1' 
  // r2 => 'res2'
  // r3 => 'res3'
});

That would break code if there is inconsistent callback that sometimes returns one parameter and other time multiple parameter.

For consistency we should always return single parameter or array of parameters. We can default to single parameter as that is most common scenario. we can allow additional options that will dictate array of parameters to be always returned (even if single parameter)
promisify(cbFun, { multiArgs: true })