var str = ‘aaabbbbcccddf‘;

        function count(str) {
            var obj = {};
            for (var i = 0, len = str.length; i < len; i++) {
                var v = str.charAt(i);
                if (obj[v] && obj[v].value == v) {
                    obj[v].count++;
                } 
 
else {
                    obj[v] = {};
                    obj[v].value = v;
                    obj[v].count = 1;
                }
            }
            for(var i in obj) {
                document.write(obj[i].value+‘ ‘+obj[i].count+‘\n‘);
            }
        }
        count(str);

計算字符串中每個字符出現的次數