feat(collections): Returns the index of the last element in the given array matching the given predicate

[getspooky]

Please see #1060

closes #1060

[kt3k]

I think we need a test case of multiple matches like findLastIndexTest([[0, 1, 2, 3, 4, 5, 6], (it) => it % 2 === 0], 6) to confirm the function actually finds the last index.

[getspooky]

@kt3k sure, I added multiple matches.

[kt3k]

@getspooky Thank you for updating! LGTM

[getspooky]

@kt3k I forgot to add documentation for findLastIndex. so i opened a PR for that #1066
thanks

[LionC]

I personally would use undefined for no index - I am aware that the native .indexOf uses -1, but all other functions within collections use undefined to communicate that nothing was found, which also has the huge benefit of forcing the consumer of the function to actually handle that case (if they are using typescript), while the current solution looks like it is fine (-1 is a number) but might blow up during runtime.

I will create a separate PR for that change.

[getspooky]

Thanks for feedback 👍🏼 ,
As you might know Array.prototype.findIndex() returns -1 indicating that no element passed the test. So i just followed the same convention provided by API.

[LionC]

I see the inspiration, however, collections is its own module and tries to be as Typescript "native" as possible, while the ES spec functions have a very historical API that cannot be changed anymore.

The same applies to filter / map functions, which have just one parameter within collections compared to their ES counterparts which have several optional parameters like index.