Function isAlphaNumeric

javascript/0125-valid-palindrome.js:72–74

(c)

 */
var isPalindrome = function (s) {
    const isAlphaNumeric = (c) =>
        (c.toLowerCase() >= 'a' && c.toLowerCase() <= 'z') ||
        (c >= '0' && c <= '9');

    let left = 0;
    let right = s.length - 1;