To replace elements in array with elements of another array with JavaScript, we use the splice method.

For instance, we write

const a = [1, 2, 3, 4, 5];
const b = [10, 20, 30];
a.splice(0, b.length, ...b);

to call a.splice with 0, b.length and the elements in b as arguments to replace the items in a between index 0 and b.length - 1 with the items in b in place.