isPalindrome.js

// recursive
const isPalindrome = str => {
  if (str.length === 0 || str.length === 1) return true
  if (str[0] === str[str.length - 1]) return isPalindrome(str.slice(1, str.length - 1))
  return false
}

// efficiently in O(n) time
const isPalindrome2 = str => {
  var half = Math.floor(str.length / 2)
  for (var i = 0; i < half; i++) {
    if (str[i] !== str[str.length - i - 1]) return false
  }
  return true
}