模拟实现JSON.stringiry 的格式化输出

前言
　　这是一道笔试题，要求模拟实现JSON.stringiry 的格式化输出,按照层级缩进，输出易读格式，即完成以下方法

JSON.stringify(jsObj, null, 4);    // 缩进4个空格

如输入：

{a:1,b:[{bb:1},{bb:2}],c:"cc"}

字符打印结果：

{
    "a": 1,
    "b": [
            {
                "bb": 1
            },
            {
                "bb": 2
            }
    ],
    "c": "cc"
}

具体实现：

 function isArray(obj) {
   if (Array.isArray) {
     return Array.isArray(obj);
   } else {
     return Object.prototype.toString.call(obj) == "[object Array]";
   }
 }

 function isObject(obj) {
   return Object.prototype.toString.call(obj) == "[object Object]";
 }

 function isString(obj) {
   return typeof obj == "string";
 }

 function isNull(obj) {
   return typeof obj == "null";
 }

 function processValue(value) {
   if (!isString(value)) {
     if (!isNull(value)) {
       return value.toString(); // 针对Number和Boolean
     } else {
       return null;
     }
   } else {
     return '"' + value.toString() + '"';
   }
 }

 function jsonStringify(value, indent) {

   var indent = indent || "";
   var ret = indent + "{\n";
   indent += "    ";
   var keys = Object.keys(value);
   for (var i = 0; i < keys.length; i++) {
     var key = keys[i];
     var v = value[key];
     ret += (indent + processValue(key) + ":");
     if (!isArray(v) || isObject(v)) {
       ret += processValue(v);
     } else {
       var ind = indent + "    ";
       for (var k = 0; k < key.length; k++) {
         ind += " ";
       }
       if (isArray(v)) {
         ret += "[\n";
         for (var j = 0; j < v.length; j++) {
           ret += jsonStringify(v[j], ind);
           if (j == v.length - 1) {
             ret += "\n";
           } else {
             ret += ",\n";
           }
         }
         ret += indent + ']';
       } else if (isObject(v)) {
         ret += jsonStringify(v, ind);
       }
     }

     if (i == keys.length - 1) {
       ret += "\n"
     } else {
       ret += ",\n"
     }
   }

   ret += indent.slice(4) + "}";
   return ret;
 }

 var result = jsonStringify({
   a: 1,
   b: [{
     bb: 1
   }, {
     bb: 2
   }],
   c: "cc"
 });
 console.log(result);