stringReverse.js

export default class Stack {
  constructor() {
    this.stack = [];
  }

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

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

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

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

  print() {
    return this.stack.join(" ");
  }

  isEmpty() {
    return this.length() === 0;
  }
}

import Stack from "./stack";

function reverseAString(str) {
  let letters = str.split("");
  let stack = new Stack();
  let reversedLetters = [];

  letters.forEach(letter => stack.push(letter));

  while (!stack.isEmpty()) {
    reversedLetters.push(stack.pop());
  }

  return reversedLetters.join("");
}

console.log(reverseAString("abcdef"));

OR just return 
str.split('').reverse().join('');

I was thinking in other ways. 😊

// Using Array.from
const stringReverse = string =>
  Array.from(string)
    .reverse()
    .join("");

// Using reduce
const stringReverse = string =>
  string
    .split("")
    .reduce((acc, curr) => [curr, ...acc])
    .join("");

// Using a for..of
const stringReverse = string => {
  let reversed = "";

  for (const char of string) {
    reversed = char + reversed;
  }

  return reversed;
};

// Using destructuring
const stringReverse = ([...string]) => string.reverse().join("");