Detecting Palindromes in javascript

isPalindrome.js

// Implement a function that will receive a string as a parameter and will return
// true or false indicating whether the text is a palindrome (spelled the same way
// forward and backwards). The solution should avoid the use of regular expressions.
function isPalindrome(text) {
  // TODO: convert accented characters to its ASCII equivalent character
  //       so it could be used by other languages.
  var allowedChars = "abcdefghijklmnopqrstuvwxyz0123456789";
  var lowercaseText = text.toLowerCase();
  var forwardWordArray = [];

  for (var i=0; i < lowercaseText.length; i++) {
    if (allowedChars.indexOf(lowercaseText[i]) >= 0)
      forwardWordArray.push(lowercaseText[i]);
  }

  return forwardWordArray.join() === forwardWordArray.reverse().join();
}

isPalindrome("race car");
//isPalindrome("Madam, I'm Adam");
//isPalindrome("browser");
//isPalindrome("012343210");