Array.map 1 element to multiple element

Question

I have [3, 16, 120]. when I do [3, 16, 120].map(mapper), I want to achieve, for example [4,5, 17,18, 121,122] i.e. each element map to n

Answer 1

Using Array.prototype.flat():

const doubled = [3, 16, 120].map(item => [item + 1, item + 2]).flat();

console.log(doubled)

Fair warning – not a standard method to this date (posted 12/2018).