$arr1 = array();
$arr1[‘username‘] = ‘test‘;
$arr1[‘age‘] = 24;
$jsonObj1 = json_encode($arr1);
// {"username":"test","age":24}

$arr2 = array();
$arr2[‘member‘][‘one‘][‘username‘] = ‘test1‘;
$arr2[‘member‘][‘one‘][‘age‘] = 26;
$arr2[‘member‘][‘two‘][‘username‘] = ‘test2‘;
$arr2[‘member‘][‘two‘][‘age‘] = 28;
$jsonObj2 = json_encode($arr2);
//  {"member":{"one":{"username":"test1","age":26},"two":{"username":"test2","age":28}}}

class test {
    public $name = "public Name";
    protected $ptName = "proctected Name";
    private $pName = "private Name";

    public function getName() {
        return $this->name;
    }
}

$Obj = new test();
$jj = json_encode($Obj);
// {"name":"public Name"}      # 只有 public变量

$j = ‘{"key": "value"}‘;

$v = json_decode($j);
var_dump($v);                   // 是一个 class

// object(stdClass)[1]
//     public ‘key‘ => string ‘value‘ (length=5)

$v = json_decode($j, true);
var_dump($v);                   // 数组类型

// array (size=1)
//     ‘key‘ => string ‘value‘ (length=5)

{ "employees": [
    { "firstName":"Bill" , "lastName":"Gates" },
    { "firstName":"George" , "lastName":"Bush" },
    { "firstName":"Thomas" , "lastName":"Carter" }
  ]
}

$json = ‘{ "employees": [
    { "firstName":"Bill" , "lastName":"Gates" },
    { "firstName":"George" , "lastName":"Bush" },
    { "firstName":"Thomas" , "lastName":"Carter" }
  ]
}‘;

$arr = json_decode($json, true);
echo $arr[‘employees‘][0][‘firstName‘];

var jsondata = ‘{"arr": [{ "name": "NAME1", "id": "ID1" }, { "name": "NAME2", "id": "ID2" }, ]}‘;

var jsonobj = JSON.parse(jsondata);
alert(jsonobj.arr[0].name);        // NAME1

$members[‘1‘][‘username‘] = ‘admin1‘;
$members[‘1‘][‘groupname‘] = ‘admin1‘;
$members[‘1‘][‘uid‘] = ‘1‘;

$members[‘2‘][‘username‘] = ‘admin2‘;
$members[‘2‘][‘groupname‘] = ‘admin2‘;
$members[‘2‘][‘uid‘] = ‘2‘;
print_r(json_encode($members));
//  {"1":{"username":"admin1","groupname":"admin1","uid":"1"},
//   "2":{"username":"admin2","groupname":"admin2","uid":"2"},}

alert(res[1][‘username‘]);     // 成功
alert(res[‘1‘][‘username‘]);   // 成功
alert(res.1.username);         // *失败*
alert(res.‘1‘.username);       // *失败*