var JsonUti = {
    //定义换行符
    n: "\n",
    //定义制表符
    t: "\t",
    //转换String
    convertToString: function(obj) {
        return JsonUti.__writeObj(obj, 1);
    },
    //写对象
    __writeObj: function(obj //对象
    , level //层次（基数为1）
    , isInArray) { //此对象是否在一个集合内
        //如果为空，直接输出null
        if (obj == null) {
            return "null";
        }
        //为普通类型，直接输出值
        if (obj.constructor == Number || obj.constructor == Date || obj.constructor == String || obj.constructor == Boolean) {
            var v = obj.toString();
            var tab = isInArray ? JsonUti.__repeatStr(JsonUti.t, level - 1) : "";
            if (obj.constructor == String || obj.constructor == Date) {
                //时间格式化只是单纯输出字符串，而不是Date对象
                return tab + ("\"" + v + "\"");
            }
            else if (obj.constructor == Boolean) {
                return tab + v.toLowerCase();
            }
            else {
                return tab + (v);
            }
        }
        //写Json对象，缓存字符串
        var currentObjStrings = [];
        //遍历属性
        for (var name in obj) {
            var temp = [];
            //格式化Tab
            var paddingTab = JsonUti.__repeatStr(JsonUti.t, level);
            temp.push(paddingTab);
            //写出属性名
            temp.push("\"" + name + "\" : ");
            var val = obj[name];
            if (val == null) {
                temp.push("null");
            }
            else {
                var c = val.constructor;
                if (c == Array) { //如果为集合，循环内部对象
                    temp.push(JsonUti.n + paddingTab + "[" + JsonUti.n);
                    var levelUp = level + 2; //层级+2
                    var tempArrValue = []; //集合元素相关字符串缓存片段
                    for (var i = 0; i < val.length; i++) {
                        //递归写对象
                        tempArrValue.push(JsonUti.__writeObj(val[i], levelUp, true));
                    }
                    temp.push(tempArrValue.join("," + JsonUti.n));
                    temp.push(JsonUti.n + paddingTab + "]");
                }
                else if (c == Function) {
                    temp.push("[Function]");
                }
                else {
                    //递归写对象
                    temp.push(JsonUti.__writeObj(val, level + 1));
                }
            }
            //加入当前对象“属性”字符串
            currentObjStrings.push(temp.join(""));
        }
        return (level > 1 && !isInArray ? JsonUti.n: "") //如果Json对象是内部，就要换行格式化
        + JsonUti.__repeatStr(JsonUti.t, level - 1) + "{" + JsonUti.n //加层次Tab格式化
        + currentObjStrings.join("," + JsonUti.n) //串联所有属性值
        + JsonUti.n + JsonUti.__repeatStr(JsonUti.t, level - 1) + "}"; //封闭对象
    },
    __isArray: function(obj) {
        if (obj) {
            return obj.constructor == Array;
        }
        return false;
    },
    __repeatStr: function(str, times) {
        var newStr = [];
        if (times > 0) {
            for (var i = 0; i < times; i++) {
                newStr.push(str);
            }
        }
        return newStr.join("");
    }
};

调用的时候用

format_str = JsonUti.convertToString(json);