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

Not particularly nice, but it is a possible solution:

var arr = [3, 16, 120];

console.log([].concat.apply([], arr.map(function (n) { return [n+1, n+2]; })));