js计算字串中每个字符出现的次数

        var arr = "helloworld";
        var obj = {};
        for (var i = 0; i < arr.length; i++) {
            var key = arr[i];
            if (obj[key]) {
                obj[key]++;
            } else {
                obj[key] = 1;
            }
        }
        console.log(obj);