How to implement a Queue in JavaScript

JavaScript, Queue, data structures

Here is a reference implementation for a Queue:

QueueTry in REPL
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function Queue() {
  this.size = 0;
  this.first = this.last = null;
}
function Node(data) {
  this.data = data;
  this.next = null;
}
Queue.prototype.add = function(data) {
  const node = new Node(data);
  if (this.last) this.last.next = node;
  this.last = node;
  if (!this.first) this.first = this.last;
  this.size++;
};
Queue.prototype.dequeue = function() {
  if (!this.first) return;
  const data = this.first.data;
  this.first = this.first.next;
  if (!this.first) this.last = null;
  this.size = Math.max(0, this.size - 1);
  return data;
};
Queue.prototype.peek = function() {
  if (!this.first) return;
  return this.first.data;
};
Queue.prototype.isEmpty = function() {
  return this.size === 0 && !this.first;
};

Tests can be found at REPL.it