Queues (FIFO)

A queue works like a line at a shop: people join at the back and are served from the front. The first item in is the first out — FIFO. The operations are enqueue (add at the back) and dequeue (remove from the front).

class Queue {
  constructor() { this.items = [] }
  enqueue(x) { this.items.push(x) }
  dequeue() { return this.items.shift() }
  get size() { return this.items.length }
}