Reverse strings in Javascript

reverse_string.js

String.prototype.reverse = function () {
  var str = this + '';

  // Check the input is invalid
  if (!str || str.length < 2 ||
    typeof str !== 'string') {
    return str;
  }

  // Take empty array revArray 
  const revArray = [];
  const length = str.length - 1;

  // Looping from the end 
  for (let i = length; i >= 0; i--) {
    revArray.push(str[i]);
  }

  // Joining the array elements 
  return revArray.join('');
};