class Stack {
    constructor() {
      this.stack = [];
    }
    
    push(el) {
        this.stack.push(el);
    }
    
    pop() {
        return this.stack.pop();
    }
  }
  
  const createStack = function () {
    const stack = [];
    const push = (el) => stack.push(el);
    const pop = () => stack.pop();
    
    return {
        push, pop
    };
  }