js findMaxDepulicateChar

function findMaxDepulicateChar(str) {
  var obj = {};
  for (let i = 0, len = str.length; i < len; i++) {
    if (!obj[str[i]]) {
      obj[str[i]] = 1;
    } else {
      obj[str[i]] += 1;
    }
  }

  var maxChar = '';
  var max = 0;
  for (var key in obj) {
    if (obj[key] > max) {
      max = obj[key];
      maxChar = key;
    }
  }

  return ('maxChar:' + maxChar + '  sum:' + max);
}


var str = 'aaaaddddddddfddfdhjjjjjjgdsbsdheldhfld';
console.log(findMaxDepulicateChar(str)); // maxChar:d  sum:15