1function palindrome(str) {
2
3    var len = str.length;
4    var mid = Math.floor(len/2);
5
6    for ( var i = 0; i < mid; i++ ) {
7        if (str[i] !== str[len - 1 - i]) {
8            return false;
9        }
10    }
11
12    return true;
13}
14

1function isPalindrome(str, ignoreSpecialChars=true) {
2  	if (typeof str !== 'string' || str.length === 0) 
3    	throw new Error("Invalid input");
4  
5  	//Here, let's first clean the string of all punctuation and weird characters
6  	function cleanString(string) {
7      	string = string.toLowerCase();
8   		const validChars = '1234567890qwertyuiopasdfghjklzxcvbnm';  
9    	let newStr = '';
10      	for (let char of string) {
11      		if (validChars.indexOf(char) > -1) {
12        		newStr += char; 
13        	}
14      	}
15      	//return a strictly alphanumeric version of the string. No spaces or other special characters.
16      	return newStr;
17    }
18  
19  	//Take note that after line 18, str will be lowercase. That's important.
20  	str = ignoreSpecialChars ? cleanString(str) : str.toLowerCase();
21  
22  	//loop only halfway through the string as we are only comparing 1st half to 2nd half
23 	for (let i = 0; i < (str.length /2); i++) {
24      	//return false if any non-match chars are found. (we're comparing lowercase to lowercase here)
25     	if (str[i] !== str[str.length - 1 - i]) 
26          return false;
27    }
28  
29  	//if loop finishes, that means it is a palindrome. So we return true
30    return true;
31}
32
33isPalindrome("Madam, I'm Adam!!") // will return true
34isPalindrome("Madam, I'm TBG, not Adam!!") // will return false
35
36isPalindrome("Madam, I'm Adam!!", false) // will return false
37isPalindrome("Racecar", false) // will return true
38

1function palindrome(str) {
2  var re = /[\W_]/g;
3  var lowRegStr = str.toLowerCase().replace(re, '');
4  var reverseStr = lowRegStr.split('').reverse().join(''); 
5  return reverseStr === lowRegStr;
6}
7palindrome("A man, a plan, a canal. Panama");

1function palindrome(str) {
2 var re = /[^A-Za-z0-9]/g;
3 str = str.toLowerCase().replace(re, '');
4 var len = str.length;
5 for (var i = 0; i < len/2; i++) {
6   if (str[i] !== str[len - 1 - i]) {
7       return false;
8   }
9 }
10 return true;
11}
12palindrome("A man, a plan, a canal. Panama");

1function palindrome(str) {
2 var splitted = str.split("");
3 var reversed = splitted.reverse("");
4 var joined = reversed.join("");
5 return joined.toLowerCase().replace(/[^0-9a-z]/gi, '') == str.toLowerCase().replace(/[^0-9a-z]/gi, '')
6}
7

1const reverseString = string.split('').reverse().join('');