回文是正反都能读通的单词、词组、数或一系列字符的序列，例如madam或racecar。

    1. function palindromeChecker(aString) {
    2.   if (
    3.     aString === undefined ||
    4.     aString === null ||
    5.     (aString !== null && aString.length === 0)
    6.   ) {
    7.     return false;
    8.   }
    9.   const deque = new Deque();
    10.   const lowerString = aString.toLocaleLowerCase().split(' ').join('');
    11.   let firstChar;
    12.   let lastChar;
    14.   for (let i = 0; i < lowerString.length; i++) {
    15.     deque.addBack(lowerString.charAt(i));
    16.   }
    18.   while (deque.size() > 1) {
    19.     firstChar = deque.removeFront();
    20.     lastChar = deque.removeBack();
    21.     if (firstChar !== lastChar) {
    22.       return false;
    23.     }
    24.   }
    26.   return true;
    27. }