how do you determine if a string is a palindrome in javascript

index.tsx
function isPalindrome(str){
  // remove non-alphanumeric characters and convert to lowercase
  str = str.replace(/[^a-zA-Z0-9]/g, '').toLowerCase();
  
  // compare first and last characters, second and second to last characters, and so on
  for(let i = 0, len = str.length; i < len / 2; i++){
    if(str[i] !== str[len - 1 - i]){
       return false; // characters do not match
    }
  }
  return true; // string is a palindrome
}

// example usage
console.log(isPalindrome("A man, a plan, a canal, Panama!")); // true
console.log(isPalindrome("Hello world")); // false
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