function rotate_left_by_one(arr) {
const arr_size = arr.length;
const first = arr[0];
for (let i = 0; i < arr_size - 1; i++) {
arr[i] = arr[i + 1];
}
arr[arr_size - 1] = first;
}
let arr = [4, 7, 2, 9, 3];
rotate_left_by_one(arr);
console.log(arr);
/*
run:
[7, 2, 9, 3, 4]
*/