/**
* @param {string} s
* @return {string}
*/varlongestPalindrome=function(s){
s = s.split('').join('#');let max =0;let start =0;let end =0;for(let i =0; i < s.length; i++){let left = i -1;let right = i +1;while(left >=0&& right < s.length){if(s.charAt(left)=== s.charAt(right)){if(max <(right - left)&& s.charAt(right)!=='#'){
max = right - left;
start = left;
end = right;}
right++;
left--;}else{break;}}}return s.slice(start, end +1).split('#').join('')};