Re:Node v8.0.0 Released
by elmigranto on Tuesday May 30, 2017 @05:40PM
(#14448759)
Almost. Don't forget about the case where callback receives multiple arguments, and the fact that someone might decide to change the API for callback signature like `(err, result)` to `(err, result, stats)`, for example.
[ Parent
| on HN ]
Promises only support a single success value so if you're "promisifying" something then you're only going to the second argument as the resolved value. The new util.promisify() doesn't provide said functionality [1] will only resolve the second argument [2] unless you define a custom function on the original function.
[1]: https://nodejs.org/api/util.html#util_util_promisify_origina...
[2]: https://github.com/nodejs/node/blob/ef16319effe396622666268c...
Re:Node v8.0.0 Released
by elmigranto on Tuesday May 30, 2017 @06:24PM
(#14449049)
A bunch of functions in core return multiple things to callback. A lot more in userland do the same. Spec or not, that is still something that needs to be accounted for.
Those are handled by `util.promisify()` by having the original function define special properties on itself `Symbol('util.promisify.custom')` and `Symbol('customPromisifyArgs')`. But it's not something handled by default (e.g. resolving an array if the callback gets more than 2 arguments passed to it).