Queue using Linked List ES6

Queue

Queue is an Abstact data structure, similar to Stacks, but differs, a queue is open at its both ends, One end is used to insert data (enque) and the other is used to removed data (dequeue). Queue follows First-in-First-Out methodology.

A real-world example is a queue of people waiting for getting vaccinated for covid. First comers will get vaccinated first.

Operations

Fundamental Operation ::
1. enqueue() -- store an item to the queue;
2. dequeue() -- remove an item from the head/first element
Auxilary operation::
1. peek() -- Get the first element with-out dequeue()
2. isfull() -- Checks if the queue is full.
3. isempty() -- Checks if the queue is empty.

Javascript implementation of Queue (Linked-List)

// Queue implementation in linked list

// Node class
class Node {
    constructor(value){
        this.value = value;
        this.next = null;
    }
}

class Queue {
    constructor(){
        this.first = null;
        this.last = null;
        this.length = 0;
    }

    peek(){
        // check if the list if empty
        if(this.length === 0 ) return 'List is empty';
        return this.first
    }
    enqueue(value){
        const newNode = new Node(value);
        // check if the list if empty
        if (this.length === 0){
            this.first = newNode;
            this.last = this.first;
        }else {
            this.last.next = newNode;
            this.last = newNode
        }
        this.length++
        return this
    }

    dequeue(){
     if(!this.first){//if first is equal null
         return 'Empty List'
     }
     if(this.first == this.last){
         this.last = null; //remove the last reference
     }
     const holding = this.first.next;
     this.first  = holding;
     this.length--;
     return this;   
    }

}

// new instance of the Queue
const queue = new Queue()
// peek 
console.log(queue.peek())
// enque first node
console.log(queue.enqueue("Gopi"))
console.log(queue.enqueue("Venkata"))
console.log(queue.enqueue("Poorna"))
// peek again
console.log(queue.peek())
// Dequeue
console.log(queue.dequeue())
console.log(queue.dequeue())
console.log(queue.dequeue())
console.log(queue.dequeue())