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 + "{
";
  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 += "[
";
        for (var j = 0; j < v.length; j++) {
          ret += jsonStringify(v[j], ind);
          if (j == v.length - 1) {
            ret += "
";
          } else {
            ret += ",
";
          }
        }
        ret += indent + ']';
      } else if (isObject(v)) {
        ret += jsonStringify(v, ind);
      }
    }

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

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



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