Longest Block in String

let input = [
    'abbCCCcddBBBxx',
   ];

let print = this.print || console.log;
let gets = this.gets || ((arr, index) => () => arr[index++])(input, 0);

let stringForCheck = gets()
let arrayofstring = Array.from(stringForCheck)
let counter = 1;
let maxCounter = 0
let sameString = ''
let arrayoffinal = []
for(let i = 0 ; i < arrayofstring.length ; i++){
    if(arrayofstring[i] == arrayofstring[i+1]){
        counter++
    } else{
        counter = 1
    }
    if(counter>maxCounter){
        maxCounter = counter
        sameString = arrayofstring[i]
    }
}
print(sameString.repeat(maxCounter))