How does `Array.from({length: 5}, (v, i) => i)` work?

Question

I may be missing something obvious here but could someone breakdown step by step why Array.from({length: 5}, (v, i) => i) returns [0, 1, 2, 3, 4]

Answer 1

On developer.mozilla.org page about array.from, nobody tell us that mapFn can take 2 arguments, for example v and k: v is value of current element, k is index of element. So here's the deal.

{length:5} create an object without any value, but with length equal to 5;

(v, k) => k is an arrow function that assign index number of current element to that element value.