无重复的最长字符串

var lengthOfLongestSubstring = function(s) {
    let arr = s.split('')
    let length = 0
    let num = 0
    
    arr.forEach((item,index)=>{
        let strArr = []
        for(let i=index;i<arr.length;i++){
            if(strArr.includes(arr[i])){
                break
            }else{
                strArr.push(arr[i])
            }
        }
        if(strArr.length>num){
            num = strArr.length
        }
    console.log(strArr)
    })
    return num
};