find max substring

max_substring.js

// find max substring
// using dynamic programming 
// Time: O(n)
var maxSubString = s => {
    if (s.length <=1) return s

    let dp = [] // max-len of the substring at index i
    var idx=0// mark start index of max substring
    dp[0] =1
    for(var i=1; i < s.length; i++){
        if(s.charAt(i) > s.charAt(i-1) 
            && s.substr(idx,dp[i-1]) < s.substring(i)){
             dp[i]=1
             idx = i
        }
        else dp[i] = dp[i-1]+1
            
    }
    return s.substr(idx,dp[s.length-1])
};


//test
console.log(maxSubString("abanbna")) //nbna
console.log(maxSubString("ababnan")) //nan
console.log(maxSubString("abcbabn")) //n