JavaScript Data Structures - Queue

Angelos Chalaris · Jul 29, 2021 ·

JavaScript, Object, Class, Array

Definition

A queue is a linear data structure that behaves like a real-world queue. It follows a first in, first out (FIFO) order of operations, similar to its real-world counterpart. This means that new items are added to the end of the queue, whereas items are removed from the start of the queue.

JavaScript Queue visualization

The main operations of a queue data structure are:

  • enqueue: Adds an element to the end of the queue
  • dequeue: Removes an element from the start of the queue
  • peek: Retrieves the element at the start of the queue, without removing it
  • isEmpty: Checks if the queue is empty

Implementation

class Queue {
  constructor() {
    this.items = [];
  }

  enqueue(item) {
    this.items.push(item);
  }

  dequeue(item) {
    return this.items.shift();
  }

  peek(item) {
    return this.items[0];
  }

  isEmpty() {
    return this.items.length === 0;
  }
}
  • Create a class with a constructor that initializes an empty array, items, for each instance.
  • Define an enqueue() method, which uses Array.prototype.push() to add an element to the end of the items array.
  • Define a dequeue() method, which uses Array.prototype.shift() to remove an element from the start of the items array.
  • Define a peek() method, which retrieves the value of the first element in the items array, without removing it.
  • Define an isEmpty() method, which uses Array.prototype.length to determine if the items array is empty.
const queue = new Queue();

queue.isEmpty();    // true

queue.enqueue('A');
queue.enqueue('B');
queue.enqueue('C');
queue.enqueue('D');
queue.enqueue('E');

queue.isEmpty();    // false

queue.peek();       // 'A'

queue.dequeue();    // 'A'
queue.dequeue();    // 'B'
queue.dequeue();    // 'C'

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