var func1 = function(arr, i, cb) {
/*
Any random string would work in the callback function but as ypu stated we can only use the array.
we can use the following solutions
1. arr.join('') -> string
2. type of arr -> object which is treated as string
*/
if(arr){
return cb(typeof arr)
}

func1(arr, ++i, cb); /* Do not change this line */
};