JS: Array.prototype.map

arrayX.map(f)

Apply function to every element of the array. Return the new array. Original array is not changed.

The function f is passed 3 args:

1. currentElement
2. currentIndex
3. arrayX

const a1 = [3, 4, 5];
const a2 = a1.map((x) => (x + 1));

console.log(a2); // [ 4, 5, 6 ]

// original is not changed
console.log(a1); // [ 3, 4, 5 ]

arrayX.map(f, thisArg)

Use thisArg for this Binding of f. If it is not given, undefined is used.

// example of using map with second argument
function ff(x) {
  return [x, this];
}
console.log([3, 4, 5].map(ff, 9));
// [ [ 3, 9 ], [ 4, 9 ], [ 5, 9 ] ]