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Comment by _bxg1 | Hacker News Reader

I like this bit of JavaScript for uniquifying an array:

  array.filter((item, index, arr) => arr.indexOf(item) === index)

It works because indexOf returns the index of the first occurrence of the item, so you're asking whether this occurrence is the first occurrence.

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Personally I like this one, although it only works for an array of primitive types.

    const unique = [...new Set(arr)];

The other advantage of the filter one is it can be stuck in the middle of a bunch of other list operations - map(), sort(), slice(), other filters(). Also, you can use findIndex() instead of indexOf() to match any arbitrary predicate, instead of exact equivalence.

Oh, for sure. I know .filter() has it's place, so if you need anything beyond making the array unique, I'd definitely use your solution.

The one I posted just blew my mind a little the first time I saw it, so I love to share it. I guess I never really considered spreading a set.

I like this neat little code to filter out falsy values:

  array.filter(Boolean)

This is O(n^2) though

All of JS's list processing functions are pretty inefficient, since at the bare minimum each one creates and copies to a new array (as opposed to, say, Rust iterators). You use them when elegance is more important than performance; N^2 is fine when N is eight.

That's always such a dangerous proposition though. Sure _you_ remember it's only fine when N is 8, but then the next guy comes along, or the input constraints change, or future you forgets because it _is_ fairly elegant looking.

I try not to leave grenades laying around too often, myself.

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