function Stack(){
  var stack = {};
  var stackSize = 0;

  return {
    push: function(item){
      stack[stackSize] = item;
      stackSize++;
    },
    pop: function(){
    	if (this.isEmpty()){ return undefined;}

      stackSize--;

    	var item = stack[stackSize];
      delete stack[stackSize];

      return item;
    },
    peek: function(){
    	if (this.isEmpty()){
      	return undefined;
      }

      return stack[stackSize - 1];
    },
    stackEmpty: function(){
      while (!this.isEmpty()){
        this.pop();
      }
    },
    isEmpty: function(){
    	return stackSize === 0;
    },
    size: function(){
    	return stackSize;
    },
    print: function(){
    	var result = [];

    	for (var key in stack){
        result.unshift(stack[key]);
      }

      return result;
    }
  }
}

const Capability = 50000000;
const TestCase = 10;
const st = new Stack();

const start = performance.now();

for (let tc = 0; tc < TestCase; tc++) {
  for (let i = 0; i < Capability; i++) {
    st.push(i);
  }

  for (let i = 0; i < Capability; i++) {
    st.pop();
  }
}

const end = performance.now();
const duration = (end - start) / TestCase;

console.log(`Duration: ${duration} ms`);