Queue Implementation using ES6

queue-es6.js

class Queue {
  constructor() {
    this.items = [];
  }
  
  enqueue(data) {
    this.items.push(data);
  } 
  
  dequeue() {
    if(this.isEmpty()){
      return "Error : Underflow"
    }
    const deletedItem = this.items[0];
    this.items.shift();
    return deletedItem;
  } 
  
  front() {
    if(this.isEmpty()){
      return "Error : Empty"
    }
    return this.items[0];
  }
  
  printQueue() {
    let queueString = '';
    this.items.forEach(function(item){
        queueString += item + " ";
    });
    return queueString;
  } 
  
  isEmpty() {
    return this.items.length === 0;
  }
  
}


const queue = new Queue();
console.log('DEQUEUE :: ' + queue.dequeue());
queue.enqueue(1);
queue.enqueue(2);
console.log('FRONT :: ' + queue.front());
queue.enqueue(3);
queue.enqueue(4);
console.log('DEQUEUE :: ' + queue.dequeue());
queue.enqueue(5);
queue.enqueue(6);
console.log('DEQUEUE :: ' + queue.dequeue());
queue.enqueue(7);
console.log('FRONT :: ' + queue.front());
console.log('QUEUE :: ' + queue.printQueue());

queue-output.txt

"DEQUEUE :: Error : Underflow"
"FRONT :: 1"
"DEQUEUE :: 1"
"DEQUEUE :: 2"
"FRONT :: 3"
"QUEUE :: 3 4 5 6 7 "