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：

 1 function isArray(obj) {
 2   if (Array.isArray) {
 3     return Array.isArray(obj);
 4   } else {
 5     return Object.prototype.toString.call(obj) == "[object Array]";
 6   }
 7 }
 8 
 9 function isObject(obj) {
10   return Object.prototype.toString.call(obj) == "[object Object]";
11 }
12 
13 function isString(obj) {
14   return typeof obj == "string";
15 }
16 
17 function isNull(obj) {
18   return typeof obj == "null";
19 }
20 
21 
22 
23 function processValue(value) {
24   if (!isString(value)) {
25     if (!isNull(value)) {
26       return value.toString(); // 针对Number和Boolean
27     } else {
28       return null;
29     }
30   } else {
31     return '"' + value.toString() + '"';
32   }
33 }
34 
35 function jsonStringify(value, indent) {
36 
37   var indent = indent || "";
38   var ret = indent + "{
";
39   indent += "    ";
40   var keys = Object.keys(value);
41   for (var i = 0; i < keys.length; i++) {
42     var key = keys[i];
43     var v = value[key];
44     ret += (indent + processValue(key) + ":");
45     if (!isArray(v) || isObject(v)) {
46       ret += processValue(v);
47     } else {
48       var ind = indent + "    ";
49       for (var k = 0; k < key.length; k++) {
50         ind += " ";
51       }
52       if (isArray(v)) {
53         ret += "[
";
54         for (var j = 0; j < v.length; j++) {
55           ret += jsonStringify(v[j], ind);
56           if (j == v.length - 1) {
57             ret += "
";
58           } else {
59             ret += ",
";
60           }
61         }
62         ret += indent + ']';
63       } else if (isObject(v)) {
64         ret += jsonStringify(v, ind);
65       }
66     }
67 
68     if (i == keys.length - 1) {
69       ret += "
"
70     } else {
71       ret += ",
"
72     }
73   }
74 
75   ret += indent.slice(4) + "}";
76   return ret;
77 }
78 
79 
80 
81 var result = jsonStringify({
82   a: 1,
83   b: [{
84     bb: 1
85   }, {
86     bb: 2
87   }],
88   c: "cc"
89 });
90 console.log(result);