Javascript Data Structure Stack in es6

class Stack {/*w w  w  . j a v a2  s . c o m*/
  constructor() {
    this.stack = [];
  }

  push(value) {
    this.stack.push(value);
  }

  pop() {
    return this.stack.pop();
  }

  peek() {
    return this.stack[this.stack.length - 1];
  }

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

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

const stack = new Stack();
stack.push(1);
stack.push(2);
stack.push(3);
stack.print(); // => 1 2 3
console.log('length is 3:', stack.length()); // => 3
console.log('peek is 3:', stack.peek()); // => 3
console.log('pop is 3:', stack.pop()); // => 3
stack.print(); // => 1 2
console.log('pop is 2:', stack.pop());  // => 2
console.log('length is 1:', stack.length()); // => 1
console.log('pop is 1:', stack.pop()); // => 1
stack.print(); // => ''
console.log('peek is undefined:', stack.peek()); // => undefined
console.log('pop is undefined:', stack.pop()); // => undefined