javascript - Why this forEach mapping is undefined?

Question

Why the result for this forEach mapping is undefined?

const list = [1, 2, 3, 4, 5, 6, 7];
const result = list.forEach(a => a % 2 === 0 ? a : -a);
console.log(result); // console prints undefined

Answer 1

forEach does not return anything. So you are getting undefined. In this case you can use map which will return an array

const list = [1, 2, 3, 4, 5, 6, 7];
const result = list.map(a => a % 2 === 0 ? a : -a);
console.log(result)