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)
