Queue Implementation in Javascript

queue-javascript.js

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

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

    enqueue(val){
        let newNode = new Node(val);
        if (this.size === 0){
            this.first = newNode;
            this.last = newNode;
        }else{
            this.last.next = newNode;
            this.last = newNode;
        }
        this.size++;
    }

    dequeue(){
        if (this.size === 0) return null;
        let node = this.first;
        if (this.size === 1){
            this.first = null;
            this.last = null
        }else{
            this.first = this.first.next;
        }
        this.size--
        return node;
    }
}

let queue = new Queue();
queue.enqueue(3);
queue.enqueue(4);
queue.enqueue(5);

queue.dequeue();