Allow resolving with a custom value

[Richienb]

Fixes #12
Fixes #22
Fixes #23

[sindresorhus]

@Richienb The method should be attached to the method, as discussed in #25 (comment)

[Richienb]

@sindresorhus

[fregante]

Not a fan of this, my suggestion used the standard method used by the Promise constructor, without having to reference pWaitFor itself

[leonsilicon]

I think an issue with using the Promise constructor is the suboptimal support for TypeScript since the types can't be auto-inferred and need to be explicitly specified with the generic argument (which isn't always practical). I believe this is a TypeScript limitation since I don't think there's a way to have the generic parameter auto-inferred in new Promise<T>(...).

[fregante]

An alternative would be to have an option deciding how to handle the returned value:

• discard (current, resolves on truthy values)
• preserve (new, resolves on non-undefined

If you want to really return undefined then you could supply a symbol: return pWaitFor.undefined

The current default where the returned value is ignored is kind of annoying.

[sindresorhus]

discard (current, resolves on truthy values)

Boolean, not truthy/falsy.

[sindresorhus]

If you want to really return undefined then you could supply a symbol: return pWaitFor.undefined

Would be a strange API.

[sindresorhus]

I personally think using a symbol-returning method for this is an elegant solution.

[sindresorhus]

This package has existed for years without the direct ability to return a value and you are the only ones that have requested it, so I don't think it's a common need either.

[sindresorhus]

We could consider some nice handling for the case of wanting the value when it's not undefined, instead of checking a boolean.

Some ideas:

import pWaitFor from 'p-wait-for';

const path = await pWaitFor.defined(async () => await getPath());

console.log(path);

import pWaitFor from 'p-wait-for';

const path = await pWaitFor(async () => {
	let path = await getPath();
	return pWaitFor.resolveIfDefined(path);
});

console.log(path);