To split an array into two based on an index in JavaScript, we use the slice method.
For instance, we write
const ar = [1, 2, 3, 4, 5, 6];
const p1 = ar.slice(0, 4);
const p2 = ar.slice(4);
to call ar.slice with 0 and 4 to return an array with the items in ar between index 0 and 3 inclusive.
And we call ar.slice with 4 to return an array with the items in ar from index 4 to the end of the ar array.
