Solution.js

const isPalindrome1 = function (s) {
    let arr1 = [],
        arr2 = [];
    for (let i = 0; i < s.length; i++) {
        if (s[i] >= "A" && s[i] <= "Z") {
            arr1.push(s[i].toLowerCase());
        }
        if ((s[i] >= "0" && s[i] <= "9") || (s[i] >= "a" && s[i] <= "z")) {
            arr1.push(s[i]);
        }
    }
    arr2 = [...arr1];
    arr2.reverse();
    return arr1.join("") === arr2.join("");
};

const isPalindrome = function (s) {
    function isNumOrAl(a) {
        if (
            (a >= "A" && a <= "Z") ||
            (a >= "0" && a <= "9") ||
            (a >= "a" && a <= "z")
        ) {
            return true;
        } else {
            return false;
        }
    }

    if (s.length === 0) {
        return true;
    }
    let i = 0,
        j = s.length - 1;
    while (i < j) {
        while (i < j && !isNumOrAl(s[i])) {
            i++;
        }
        while (i < j && !isNumOrAl(s[j])) {
            j--;
        }
        if (s[i].toLowerCase() !== s[j].toLowerCase()) {
            return false;
        } else {
            i++;
            j--;
        }
    }
    return true;
};