最长回文子串

function longestPalindrome(s) {
    if(s.length == 0){
        return s
    }
    let palindrome = s[0]
    for(let i = 0;i < s.length -1;i++){
        let item = s[i]
        let substr = item
        for(let j = i+1;j < s.length;j++){
            let jItem = s[j]
            substr += jItem
            if(substr.length == 2 && jItem == item && substr.length > palindrome.length){
                palindrome = substr
            }else{
                if(substr == substr.split(‘‘).reverse().join(‘‘) && substr.length > palindrome.length ){
                    palindrome = substr
                }
            }
        }
    }
    return palindrome
}