function Queue() {
  this.collection = [];

  // print the queue collection
  this.print = function () {
    return this.collection;
  };

  this.enqueue = function (element) {
    this.collection.push(element);
  };

  this.dequeue = function () {
    this.collection.shift();
  };

  this.front = function () {
    return this.collection[0];
  };

  this.size = function () {
    return this.collection.length;
  };

  this.isEmpty = function () {
    return this.collection.length === 0;
  };
};

const myQueue = new Queue();
myQueue.enqueue(10);
myQueue.enqueue(20);
myQueue.enqueue(30);

console.log(myQueue.print());
console.log(myQueue.front());
myQueue.dequeue();
console.log(myQueue.print());
console.log(myQueue.size());
console.log(myQueue.isEmpty());
myQueue.dequeue();
myQueue.dequeue();
console.log(myQueue.isEmpty());