most popular letter in str javascript

1var getMax = function (str) {
2 var max = 0,
3     maxChar = '';
4  str.split('').forEach(function(char){
5    if(str.split(char).length > max) {
6        max = str.split(char).length;
7        maxChar = char;
8     }
9  });
10  return maxChar;
11};