function shiftArray(arr) {
  // remove 1 item at 0-index position, return the deleted item
  return arr.splice(0, 1);
}

var a = [1, 2, 3];

var b = a.shift();

console.log(a); // [2, 3]

console.log(b); // 1

var c = shiftArray(a);

console.log(a); // [3]

console.log(c); // [2]