Javascript Data Structure Queue in es6

class Queue {//  ww  w .java  2 s  .  c  om
  constructor() {
    this.queue = [];
  }

  enqueue(value) {
    this.queue.push(value);
  }

  dequeue() {
    return this.queue.shift();
  }

  peek() {
    return this.queue[0];
  }

  length() {
    return this.queue.length;
  }

  print() {
    console.log(this.queue.join(' '));
  }
}

const queue = new Queue();
queue.enqueue(1);
queue.enqueue(2);
queue.enqueue(3);
queue.print(); // => 1 2 3
console.log('length is 3:', queue.length()); // => 3
console.log('peek is 1:', queue.peek()); // => 3
console.log('dequeue is 1:', queue.dequeue()); // => 1
queue.print(); // => 2 3
console.log('dequeue is 2:', queue.dequeue());  // => 2
console.log('length is 1:', queue.length()); // => 1
console.log('dequeue is 3:', queue.dequeue()); // => 3
queue.print(); // => ''
console.log('peek is undefined:', queue.peek()); // => undefined
console.log('dequeue is undefined:', queue.dequeue()); // => undefined