FP techniques that will help you write better JavaScript

Re:FP techniques that will help you write better JavaScript by nefitty on Friday February 11, 2022 @04:44AM (#30299348)

I basically rely on map 80% of the time for iteration. I do have to spend some mental cycles on deciding where to go if I needed to break or skip elements. That was until I discovered the beautiful .flatMap() trick of returning an empty array to skip or exclude an index item.

Is it bad to use map?

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Re:FP techniques that will help you write better JavaScript by bluefirebrand on Friday February 11, 2022 @09:39AM (#30301970)

I see people use JavaScript Array.map a lot when they aren't doing anything with the returned array, which I find kind of irritating.

So if you're using map sensibly, no there's nothing wrong. But I don't like the dogma I read a lot which is "use map always" because it leads to inexperience developers using it in the wrong circumstances.

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Re:FP techniques that will help you write better JavaScript by Akronymus on Friday February 11, 2022 @10:08AM (#30302278)

Does JS have something like array.iter?

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Re:FP techniques that will help you write better JavaScript by yakshaving_jgt on Friday February 11, 2022 @05:03AM (#30299486)

What are you struggling with when trying to skip elements?

> Is it bad to use map?

No.

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Re:FP techniques that will help you write better JavaScript by nefitty on Friday February 11, 2022 @05:25AM (#30299664)

Whether to use a for loop or for of or forEach or map().filter() etc

flatMap takes care of a lot of that

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Re:FP techniques that will help you write better JavaScript by yakshaving_jgt on Friday February 11, 2022 @05:29AM (#30299692)

Why are you using a “trick” to skip an element in some structure when mapping a function over it?

For posterity (and forgive me if this JavaScript syntax is inaccurate; I don't write it so much these days)…

    xs.map(a => shouldBeSkipped ? a : f(a))

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Re:FP techniques that will help you write better JavaScript by wlamartin on Friday February 11, 2022 @09:34AM (#30301917)

They don't want to keep the unmapped value in the resulting collection at all. flatMap allows for removal of an element in one traverse, unlike filter+map with eager behaviour.

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Re:FP techniques that will help you write better JavaScript by yakshaving_jgt on Friday February 11, 2022 @09:38AM (#30301964)

Then why not just use a fold?

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Re:FP techniques that will help you write better JavaScript by wlamartin on Friday February 11, 2022 @10:09AM (#30302287)

Sure, there's many ways to skin a cat. Given the option, I wouldn't choose either of these, and instead use something like filterMap[1] which I think conveys intent better than a fold or flatMap.

Btw, I'm assuming that the original map questioner wasn't solely using flatMap for side-effectful iteration, which reading again, I'm a bit suspicious about.

1: https://gcanti.github.io/fp-ts/modules/Array.ts.html#filterm...

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