don't check mapFn length

[AlexErrant]

In the course of writing <SetEntries>, I did a bit of digging on something I found confusing, resulting in this PR.

I'm not sure why we need to check the parameter count of the mapFn:

solid-primitives/packages/keyed/src/index.ts

Lines 230 to 237 in 71f6c5e

	mapFn.length < 3
	? key =>
	(mapFn as (key: K, v: Accessor<V>) => JSX.Element)(
	key,
	() => (props.of as Map<K, V>).get(key)!,
	)
	: (key, i) => mapFn(key, () => (props.of as Map<K, V>).get(key)!, i),
	"fallback" in props ? { fallback: () => props.fallback } : undefined,

Without types for easier reading:

mapFn.length < 3
    ? (key   ) => mapFn(key, () => props.of.get(key))
    : (key, i) => mapFn(key, () => props.of.get(key), i),

The mapFn is user-defined and may take 2 or 3 parameters. However, I believe that this is irrelevant and can be simplified to

(key, i) => mapFn(key, () => props.of.get(key), i),

You can see that in the following code, if you pass 3 arguments to a function that has 2 parameters, the 3rd argument is ignored:

let xs = ["a", "b", "c"]

const userFn2 = (key: string, val: string) => {
    return [key, val]
}

const userFn3 = (key: string, val: string, i: number) => {
    return [key, val, i]
}

console.log("userFn2       ", xs.map(x      => userFn2(x, x)))
console.log("userFn3       ", xs.map((x, i) => userFn3(x, x, i)))
console.log("userFn2 with 3", xs.map((x, i) => userFn2(x, x, i)))
//[LOG]: "userFn2       ",  [["a", "a"], ["b", "b"], ["c", "c"]] 
//[LOG]: "userFn3       ",  [["a", "a", 0], ["b", "b", 1], ["c", "c", 2]] 
//[LOG]: "userFn2 with 3",  [["a", "a"], ["b", "b"], ["c", "c"]]

Playground.

This demos what happens when the user gives us a fn with 2 parameters, but solid-primitives gives it 3 arguments.

Relevant StackOverflow.

Perhaps I'm missing something obvious - I'm not super experienced with JS 😅

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[thetarnav]

Check the source for mapArray
it doesn't create signals for index if the user does not use it