不含重复字符的最长子字符串

思路

var lengthOfLongestSubstring = funtion(s){
	// 初始化最大值、长度
    let max = 0;
    let len = s.length;
    let str = '';
    for(let i = 0; i < len; i++){
        let index = str.indexOf(s[i])
        if(index != )
    }
    str = 
}