地址：http://ysm.missed.com.cn/game/maxstr.html 实现了三种方法

方法一

采用循环的方式，找出每个位置对应的最大字符串长度

 function lengthOfLongestSubstring(s) {
    var data = s.split('');
        var tempmax = 1;
        if(!data.length){return 0;}
        for(var i=0;i<data.length;i++){
              var str_arr = new Array();
              str_arr.push(data[i]);
              for(var j=(i+1);j<data.length;j++){
                   if(data[j]==data[i]){
                        
                        var temp = j-i;
                        if(tempmax<temp){
                            tempmax = temp;
                        }
                        break;
                   }else{
                         if(str_arr.indexOf(data[j])==-1){
                            temp2 = j-i+1;
                            str_arr.push(data[j]);
                            if(tempmax<temp2){
                                tempmax = temp2;
                            }
                         }else{
                            break;
                         }

                   }
              }
        }
         console.log(tempmax);
        return tempmax;
   };

方法二

非常精妙的方法

function lengthOfLongestSubstring2(s){
    let stack = [], m = s.split(''), ticker = 0, maxCount = 0, i = 0
    
    for(i; i < m.length; i++) {
        let cur = m[i], q = stack.indexOf(cur)
        if (q == -1) {
            stack.push(cur)
            ticker = stack.length
            if (ticker > maxCount) {
                maxCount = ticker
            }
        } else {
            stack.splice(0, q + 1)
            stack.push(cur)
            ticker = stack.length
        }
    }
    console.log(maxCount);
    return maxCount

}

方法三

和方法二类似

 function lengthOfLongestSubstring3(s) {
    if(s===""){return 0};
    var arr = s.split("");
    var newarr = [ arr[0] ];
    var newstr = arr[0];
    var length =1; //字符串的长度
    var index = 0; //重复下标
    var substr = ""; //截取之后的字符串

    for (var i = 0; i< arr.length-1; i++){
 
            newstr = newarr.join("");
       
            index = newstr.indexOf(arr[i+1]);
 
            //下一位与之前的字符串是否有某个字节相同
            if(index > -1){
                length = Math.max(newstr.length,length);
                newstr = newstr + arr[i+1];
                substr = newstr.substring(index+1);

                newarr = substr.split("");

            }else{
                newarr.push(arr[i+1]);

            }

    }
    return (Math.max(length,newarr.length));
    
};