b.js

function main(str) {
  var mid = str.length>>1;
  for(var i = 0;i<mid;++i) {
    if(str[i] !== str[str.length-1-i]) return false;
  }
  return true;
}
console.log(main('anitalavalatina'));
console.log(main('a'));
console.log(main('aaabbbbbbaaa'));
console.log(main('aaabbbxbbbaaa'));
console.log(main('aaabbb'));
console.log(main('aaaxbbb'));
console.log(main('aabbb'));