解码时的Javascript标记、JWT和数字

我对使用JWT和令牌是完全陌生的;我只是想这么做:

console.log("logged " + data);  

//prints { _id: 5a82ee98e918b22e83d6c3e0,
//username: 'test2',
//name: 'test',
//surname: '2',
//password: '...'
//[etc]
 //}

console.log("logged _id " + data._id);

//prints 5a82ee98e918b22e83d6c3e0

var token = jwt.sign(data._id, secret, {
                    expiresIn: "24h" // expires in 24 hours
                });
console.log("saved token " + token);

//prints the token in style eyJhbGciOi[...].eyJfYnNvbn[...].usoLRz-[...]


console.log("decoded: " + JSON.stringify( jwt.decode(token) ) )


//prints the token in this way:
//{"_bsontype":"ObjectID","id":{"type":"Buffer","data":[90,130,238,152,233,24,178,46,131,214,195,224]},"iat":1519502719,"exp":1519589119}

1. 为什么不以纯文本形式打印id号?
2. 如何获取我在令牌中输入的id号?

更新: 我在一个登录功能;数据是登录后的答案,包含登录用户;我有

var login = function(req, res) { 
    passport.authenticate('local', function(err, data, info) { 
        if (err) { console.log(err); 
    } 
    console.log("data in auth " + data);
    if (!data) { 
        return res.status(404); 
    } 
    req.logIn(data, function(err) { 
        if (err) { 
            console.log("err " + err); 
        } 
        console.log("logged " + data);
        console.log("logged _id " + data._id);
        var token = jwt.sign[continues on top]
    [...]
}