Javascript 查找字符串中出现最多的字符和出现的次数

<script type="text/javascript">
    //查找字符串中出现最多的字符和出现的次数
    var str = 'Thatwheneying its on security.';
    function find(str) {
        var max = 0, c;
        while(str) {
            var char = str.charAt(0);
            var a = str.split(char);
            var count = str.length - (str = a.join("")).length;
            if(count > max) {
                max = count;
                c = char;
            }
        }
        return {"max":max, "char":c};
    }
    console.log(find(str));
</script>