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

You could use Array#reduce in combination with Array#concat.

console.log([3, 16, 120].reduce(function (r, a) {
    return r.concat(a + 1, a + 2);
}, []));

ES6

console.log([3, 16, 120].reduce((r, a) => r.concat(a + 1, a + 2), []));