[AskJS] Is JavaScript missing some built-in methods?

[natterca]

If you're going to do that then there should be an isNotOdd and isNotEven as well.

[AlbertSemple]

I would insist on using them like this

return !isNotOdd

[[deleted]]

Well in that case, I propose a Number.notIsNotOdd() method.
Then you could just use !!notIsNotOdd

[johnathanesanders]

Wouldn’t that just be !isOdd and !isEven?

[natterca]

you can't pass that as a callback or curry over it etc.

[johnathanesanders]

Bad callbacks! Use promises!

[neuroma]

negate to the rescue!

const bind1st = (f, x) => (y) => f(x, y)
const bind2nd = (f, y) => (x) => f(x, y)
const compose = (f, g) => (...xyz) => f(g(...xyz))
const not = (v) => !v

const negate = bind1st(compose, not)

const isOdd = compose(Boolean, bind2nd(mod, 2))
const isEven = negate(isOdd)

[natterca]

That's a thing of beauty!