Methods for keeping this

[LinusU]

I find that I quite often need to preserve this when calling functions that takes callbacks. I have used something similar to the code below, but I would like to hear what you think of the matter.

Is there an easy way to support this use case?

function promise (obj, fn) {
  return pify(obj[fn]).bind(obj)
}

await promise(linus, 'walk')(100, 'miles')
console.log('Linus walked 100 miles')

// vs.

linus.walk(100, 'miles', () => console.log('Linus walked 100 miles'))

[SamVerschueren]

Just use bind directly.

await pify(linus.walk.bind(linux))(100, 'miles');

[LinusU]

That's true, I guess that it would be even nicer if pify supported it out of the box though. Maybe it's outside the scope though...

await pify(linus, 'walk')(100, 'miles')

[sindresorhus]

@LinusU How would it know what to bind to? You would have had to pass the this in anyways.

[SamVerschueren]

@sindresorhus He wants that this example

await pify(linus, 'walk')(100, 'miles')

binds the walk method to the linus object and thus to itself. But this was discussed in the past if I'm not mistaken.

[sindresorhus]

Yeah, not worth saving just a few characters. Using bind is a lot clearer too.

[LinusU]

Yes, what @SamVerschueren said, I should have been more clear.

I don't know if it's the cleanest approach, my main goal is just to keep the code clean and readable. I guess that we are at a point where many libraries are transitioning into promises, but it will probably be a long time until we are all the way there.

The problem I see with doing, e.g. pify(fs.readFile) is that I make an assumption that readFile doesn't use this. It seems like this will creep up to bite me at some point, which is why I would prefer to solve it somehow...

The function bind operator could solve this by using pify(::fs.readFile), but that isn't nowhere near ready though :)

[SamVerschueren]

With using bind, you can bind the method to whatever you want so it's much more flexible and it's clear for everyone that it is bound to the object you pass in.

I make an assumption that readFile doesn't use this. It seems like this will creep up to bite me at some point.

Your tests should catch that.

[sindresorhus]

I've rarely encountered the need to use bind though. Most API's in the Node.js world are luckily not using this.

[LinusU]

I've rarely encountered the need to use bind though. Most API's in the Node.js world are luckily not using this.

True, I guess that this is good enough for now 👍 thanks for the discussion