myQueue_LL.js

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

    // Peek the first element in line
    peek() {
        this.length ? console.log(`First in Line = ${this.first.value}`) : console.log('Queue is empty');
        return this.length;
    }

    // Print the elements in the queue.	
    printList() {
        let list = [];
        let currentNode = this.first;
        while(currentNode !== null) {
            list.push(currentNode.value);
            currentNode = currentNode.next;
        }
        console.log(list.join(' --> '));
        return this.length;
    }

    // Add element at the end of the queue.
    enqueue(value) {
        let newNode = new Node(value);

        if (this.length) {
            this.last.next = newNode;
            this.last = newNode;
        } else {
            this.first = newNode;
            this.last = newNode;
        }

        this.length++;

        return this.printList();
    }

    // Remove the fist element in the queue.
    dequeue() {
        if (this.length) {
            const tempNode = this.first;
            this.first = this.first.next;

            console.log(`Dequeued ${tempNode.value}`);
            this.length--;
        } else {
            this.last = null;
            console.log('Queue is empty');
        }

        return this.length;
    }
  }
  
const myQueue = new Queue();

myQueue.peek();                    // Queue is empty

myQueue.enqueue('Rachel');         // Rachel
myQueue.enqueue('Ross');           // Rachel --> Ross  
myQueue.enqueue('Monica');         // Rachel --> Ross --> Monica
myQueue.enqueue('Joey');           // Rachel --> Ross --> Monica --> Joey

myQueue.peek();                    // First in Line = Rachel

myQueue.dequeue();                 // Dequeued Rachel
myQueue.dequeue();                 // Dequeued Ross
myQueue.dequeue();                 // Dequeued Monica
myQueue.dequeue();                 // Dequeued Joey
myQueue.dequeue();                 // Queue is empty