A palindrome is a word, phrase, or number that is spelled the same forward and backward. For example, “dad” is a palindrome; “A man, a plan, a canal: Panama” is a palindrome if you take out the spaces and ignore the punctuation; and 1,001 is a numeric palindrome. We can use a stack to determine whether or not a given string is a palindrome.
Write a function that takes a string of letters and returns true or false to determine whether it is palindromic. For example:
function is_palindrome(s) {
s = s.toLowerCase().replace(/[^a-zA-Z0-9]/g, "");