var str = 'aadbbcaffg';
        var obj = {};
        var arr = [], arr2 = [];
        var temp_name, temp_v;
        for (var x=0; x<str.length; x++) {
            if (!obj[str[x]]) {
                obj[str[x]] = 1;
                arr.push(str[x]);
            } else {
                obj[str[x]]++;
            }
        }
        while (arr.length > 1) {
            temp_name = arr[0];
            temp_v = obj[arr[0]];
            for (var i=1; i<arr.length; i++){
                if (temp_v < obj[arr[i]]){
                    temp_name = arr[i];
                    temp_v = obj[arr[i]]
                }else if (temp_v === obj[arr[i]]) {
                    if (temp_name.charCodeAt() > arr[i].charCodeAt()) {
                        temp_name = arr[i];
                        temp_v = obj[arr[i]]
                    }
                }
            }
            arr2.push([temp_name, temp_v]);
            arr.splice(arr.indexOf(temp_name), 1);
        }
        console.log(arr);
        arr2.push([arr[0], obj[arr[0]]]);
        console.log(arr2);