palindrome_dm.js

'use strict'; // avoid ambiguity and sloppy errors

/**
 * Tests wether or not a given string is a Palindrome
 * @param {string} stringToTest - the string to test.
 */
function isPalindrome(stringToTest) {
  var start = 0,
    end,
    firstChar,
    lastChar,
    valid;

  // make sure we have a string.
  if (typeof stringToTest !== "string") {
    // throw if we didn't get a string
    throw new TypeError("isPalindrome() expected a string, but got " +
      Object.prototype.toString.call(stringToTest) + " instead!");
  }

  if (/^[^a-z0–9]*$/i.test(stringToTest)) {
    // warn if we have no valid characters to test
    console.log("No valid characters to test, treated as empty string" +
      "\nStack: \n" + new Error().stack);
    return true; // an empty string is a palindrome.
  }

  end = stringToTest.length - 1;
  // compare characters from outside in. stop when we get to the middle.
  while (start < end) {
    firstChar = stringToTest[start].toLowerCase();
    lastChar = stringToTest[end].toLowerCase();
    valid = true;

    if (/[^a-z0-9]/.test(firstChar)) {
      start++;
      valid =false;
    }
    
    if (/[^a-z0-9]/.test(lastChar)) {
      end--;
      valid=false;
    } 
    
    if(valid) {
	    if(firstChar === lastChar) {
	      start++;
	      end--;
	    } else {
	      return false;
	    }
    }
  }

  // if we get here, it's a palindrome
  return true;
}

// tests (should be in a seperate file using a test framework)
console.log(isPalindrome("something that is not a palindrome") + " = false");
console.log(isPalindrome("something that is \n not a palindrome") + " = false");
console.log(isPalindrome("race \n car") + " = true");
console.log(isPalindrome("") + " = true");
console.log(isPalindrome("  ") + " = true");
console.log(isPalindrome("1221") + " = true 1221");
console.log(isPalindrome("0") + " = true");
console.log(isPalindrome("racecar") + " = true");
console.log(isPalindrome("No 'x' in Nixon!") + " = true");
console.log(isPalindrome("~~!~!~") + " = true + warn");
console.log(isPalindrome("Momsie") + " = false");
console.log(isPalindrome(12) + " = warn + false");
console.log(isPalindrome(undefined) + " = warn + false");
console.log(isPalindrome(null) + " = warn + false null");