stack using LinkedList / array

stack.js

// using LinkedList

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  };
}

class Stack {
  constructor() {
    this.top = null;
    this.bottom = null;
    this.length = 0;
  }

  push(value) {
    const newNode = new Node(value);
    if (this.length === 0) {
      this.top = newNode;
      this.bottom = newNode;
    } else {
      let holdingPointer = this.top;
      this.top = newNode;
      this.top.next = holdingPointer;
    }
    this.length += 1;
    return this;
  };

  peek() {
    return this.top;
  } 

  pop() {
    if (!this.top) {
      return null;
    } else {
      const holdingPointer = this.top;
      this.top = this.top.next;
      this.length -=1;
      return holdingPointer
    }
    // return this;
  }

}

const stack = new Stack();
stack.push('google');
stack.push('google1');
stack.peek();
stack.pop();

// using Array

class StackArray {

  constructor() {
    this.array = [];
  }

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

  push(value) {
    return this.array.push(value);
  };

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

}

const stack = new StackArray();
stack.push('google1');
stack.push('google2');
stack.push('google3');
stack.peek();
stack.pop();