const firstFIFO = [];
const secondFIFO = [];

const LIFO = {
  enqueue: (object => {
    firstFIFO.push(object);
  }),

  dequeue: (() => {
    if (firstFIFO.length === 0 && secondFIFO.length === 0) return null;

    while (firstFIFO.length !== 1) {
      secondFIFO.push(firstFIFO.shift());
    }

    const result = firstFIFO.pop();

    while (secondFIFO.length) {
      firstFIFO.push(secondFIFO.shift());
    }

    return result;
  })
}


LIFO.enqueue(1);
LIFO.enqueue(2);
LIFO.enqueue(3);
LIFO.enqueue(4);
console.log(LIFO.dequeue());
console.log(LIFO.dequeue());
console.log(LIFO.dequeue());
LIFO.enqueue(5);
console.log(LIFO.dequeue());
console.log(LIFO.dequeue());