如何利用js知道次数最多的字符及其次数

var getMax = (str) => { 
 var o = {}; 
 for(var i in str){
 o[str[i]] ? o[str[i]]++ : o[str[i]] = 1; 
 } 
 var keys = Object.keys(o); 
 var values = Object.values(o); 
 var maxVal = Math.max.apply(Math,values);
 console.log(keys[values.indexOf(maxVal)],maxVal);
}
getMax('aaabbbbcddeefggggggggggghijjjggk') // g 13
getMax('aaabbbbcddeefggggggggggghijjjk') // g 11
getMax('aaabbggggggggbbcddeefggggggggggghijjjk') // g 19