Check if a string is a palindrome. JavaScript implementation

palindrome.js

//v1 without built in functions
function palindrome(str) {
    var len = str.length,
      mid = Math.floor(len/2);
      
    for ( var i = 0; i < mid; i++ ) {
        if (str[i] !== str[len - 1 - i]) {
            return false;
        }
    }
    return true;
}

//v2 with built in functions
function isPalindrome(s) {
    return s == s.split("").reverse().join("") ? true : false;
}