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A comment on Node v8.0.0 Released. Parent comment

Re:Node v8.0.0 Released by idbehold on Tuesday May 30, 2017 @05:22PM (#14448654)
Promisify is a super simple function to write yourself though.

  const promisify = (fn, ctx) => (...args) =>
    new Promise((resolve, reject) =>
      fn.apply(ctx, [ ...args,
        (err, data) => err ? reject(err) : resolve(data)
      ])
    )
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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.
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Re:Node v8.0.0 Released by idbehold on Tuesday May 30, 2017 @06:19PM (#14449008)
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...

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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.
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Re:Node v8.0.0 Released by idbehold on Tuesday May 30, 2017 @06:33PM (#14449107)
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).
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Re:Node v8.0.0 Released by bfred_it on Wednesday May 31, 2017 @07:43AM (#14451711)
But why. If you're gonna take special steps to handle `util.promisify` you might as well just offer a Promised API and skip `util.promisify`
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Re:Node v8.0.0 Released by rattray on Tuesday May 30, 2017 @08:42PM (#14449734)
The problem is that everyone does that slightly differently.

Having a stdlib function makes for an easy "let's just use this everywhere" answer.

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