微信小程序如何获取用户的openid

//app.js
App({
  onLaunch: function() {
    wx.login({
      success: function(res) {
        if (res.code) {
          //发起网络请求
          wx.request({
            url: 'https://test.com/onLogin',
            data: {
              code: res.code
            }
          })
        } else {
          console.log('获取用户登录态失败！' + res.errMsg)
        }
      }
    });
  }
})

//获取用户openid
function getopenid(){
	$js_code = I('post.code');
	if(empty($js_code)) return array('status'=>0,'info'=>'缺少js_code');
	
	$appid = 'xxxxxxxxxxxxx';
	$appsecret = 'xxxxxxxxxxxxxxxxxxxxxx';
	$curl = 'https://api.weixin.qq.com/sns/jscode2session?appid=%s&secret=%s&js_code=%s&grant_type=authorization_code';
	$curl = sprintf($curl,$appid,$appsecret,$js_code);
	$result = request($curl);
	return array('status'=>1,'info'=>json_decode($result,true));
}

//正常返回的JSON数据包
{
      "openid": "OPENID",
      "session_key": "SESSIONKEY",
      "unionid": "UNIONID"
}
//错误时返回JSON数据包(示例为Code无效)
{
    "errcode": 40029,
    "errmsg": "invalid code"
}