A queue is a simpledata structure that allows elements to be inserted from one end, called the rear (also called tail), and deleted from the other end, called the front (also called head).

This behavior is calledFIFO(First in First Out).

So, a queue is a linear data structure. A very important concept is that a queue deletes only theoldest added element.

The person that is removed was the first in the queue

Applications

• Queues are used whenever we need to manage objects in order starting with the first one in.
• Scenarios include printing documents on a printer, call center systems answering people on hold people, and so on.

Creation

• A queue can be implemented using anarray or alinked list.

So, in JavaScript doing aQueue is very simple because we can take arrays methods, likeunshift andpop.

Remember :

unshift Adds a element to the beginning of the array.pop Deletes the last element of the array.

Implementation

So the first thing that we are going to do is create a Queue constructor function with a empty array inside.

function Queue() {this.data = [];}

Remember that we use thethis keyword there because we need to pointer the object that we create.

Methods

The main methods will beadd andremove:

Queue.prototype.add = function(record) {this.data.unshift(record);}

Queue.prototype.remove = function() {this.data.pop();}

And we are going to add 3 methods more:

Queue.prototype.first = function() {return this.data[0];}

Queue.prototype.last = function() {return this.data[this.data.length - 1];}

Queue.prototype.size = function() {return this.data.length;}

So, let’s see what we get:

const q = new Queue():q.add(1);q.add(2);q.add(3);console.log(q);

So, the oldest one is the element with the value of1 because we added it first.

If you don’t believe me, you can use ourlast method to see it:

console.log(q.first());// -> 3console.log(q.last());// -> 1

So if we use theremove method the element that will be deleted is the oldest so the 1 is out.

q.remove();console.log(q);

And we have the last method callsize

console.log(q.size())// -> 2

Return ‘‘2’’ after we delete the last element.