一道算法题

对String做扩展，实现如下方式获取字符串中频率最高的字符

var str = 'ahbbccdeddddfg';
var ch = str.getMostOften();
console.log(ch); //d , 因为d 出现了5次

  var str = 'ahbbccdeddddfg'
  String.prototype.getMostOften = function(){
    var obj = {}
    for(var i = 0; i<str.length; i++){
      var letter = str.charAt(i)
      if(!obj[letter]){
        obj[letter] = 1
      }else{
        obj[letter]++
      }
    }
    console.log(obj)
    var maxIdx = 0
    var maxLetter = ''
    for(var key in obj){
      if(maxIdx < obj[key]){
        maxIdx = obj[key]
        maxLetter = key
      }
    }
    return maxLetter
  }
  var ch = str.getMostOften()
  console.log(ch)