Queue.js

// Queue class
class Queue {
    // Array is used to implement queue
    constructor() {
        this.items = [];
    }

    // enqueue function
    enqueue(element) {
        // Adding element to the queue
        this.items.push(element);
    }

    // dequeue function
    dequeue() {
        // removing element from the queue
        // return underflow when called
        // on empty queue
        if (this.isEmpty()) {
            return "Underflow";
        }
        return this.items.shift();
    }

    // front function
    front() {
        // return the front element of
        // the queue without removing it
        if (this.isEmpty()); {
            return 'No elements in Queue';
        }
        return this.items[0];
    }

    // isEmpty function
    isEmpty() {
        // return true if queue is empty
        return this.items.length == 0;
    }

    // printQueue function
    printQueue() {
        return this.items;
    }
}

var queue = new Queue();
var bool = true;
while (bool) {
    var userInput = prompt('Enter Choice (enqueue, dequeue, front, end, print)...');
    switch (userInput.toLowerCase()) {
        case 'enqueue':
            {
                queue.enqueue(prompt('Enter Element'));
                break;
            }
        case 'dequeue':
            {
                if (queue.isEmpty()) {
                    alert('Queue is Empty!!');
                } else {
                    alert(`Dequeued Element : ${queue.dequeue()}`);
                }
                break;
            }
        case 'front':
            {
                if (queue.isEmpty()) {
                    alert(`Queue is Empty!!`);
                } else {
                    alert(`Front element of Queue : ${queue.front()}`);
                }
                break;
            }
        case 'end':
            {
                bool = false;
                break;
            }
        case 'print':
            {
                alert(queue.printQueue());
                break;
            }
        default:
            bool = confirm('Invalid Choice!! Do you want to try again...');
    }
}

// Print Queue
if (queue.isEmpty()) {
    document.write(`Queue is Empty!!`);
} else {
    document.write(`Queue : ${queue.printQueue()}`);
}