How to define a callback-Function in own Function? NodeJS

Question

I'm pretty new in nodeJS and came around the following problem: I defined a Function in one of my Controllers, which I want to verify a JSON-Web-Token. I used the following function:

exports.validate = function (token, cb) {
   jwt.verify(token, secretToken, cb(err, decoded));
}

But everytime I want to run it, nodeJS gives me the error, that 'err' is not defined? In the jwt-Example there's following example:

// verify a token symmetric
jwt.verify(token, 'shhhhh', function(err, decoded) {
   console.log(decoded.foo)
});

So somewhere obviously I went wrong, but I don't know what. I also have no Idea what to look for... I've done some Google searches, but nothing helped me so far.

I would love to hear from you.

Regards

//EDIT: That's how I call the function:

AuthController.validate(req.headers['api-token'], function(err, decoded){ 
if(err){ console.log('Error: ', err);
   res.status(401); next(); 
} else if(decoded) { 
   console.log('Success: ', decoded); 
   next(); 
} 
})

I don't understand? Which function do you mean? Like I said, I'm pretty new to nodeJS. Maybe I didn't understand the concept of callbacks correctly. How would you have done it? — mietzekotze
– mietzekotze, Commented Jun 29, 2014 at 20:16
There's nothing Node specific here, callbacks are a pretty common JavaScript pattern. — Quentin
– Quentin, Commented Jun 29, 2014 at 20:17

Quentin · Accepted Answer · 2014-06-29 20:15:41Z

2

In the jwt-Example, the third argument to verify is a function (created using a function expression).

In your code, the third argument is the return value or calling cb(err, decoded). The cb function might return a function, but err is a variable you are passing to it.

If you want to use a function called cb then define it and then pass the function:

function cb(err, decoded) {
    // do stuff with err and/or decoded
}
jwt.verify(token, secretToken, cb);

answered Jun 29, 2014 at 20:15

Quentin

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2 Comments

mietzekotze Over a year ago

That's what I do. Here's how i use it: AuthController.validate(req.headers['api-token'], function(err, decoded){ if(err){ console.log('Error: ', err); res.status(401); next(); } else if(decoded) { console.log('Success: ', decoded); next(); } });

mietzekotze Over a year ago

I updated my first post, to include it. I understood the concept so far, and thats why I don't understand, why the above doesnt work. As far as I see, I did everything right.

cvng · Accepted Answer · 2014-06-29 21:40:59Z

0

If you want your function to work with callback it should use it this way:

exports.validate = function (token, cb) {

    jwt.verify(token, secretToken, function (err, decoded) {
        if (err)
            return cb(err, null);

        // callback have to handle error
        return cb(null, decoded);
    }
}

answered Jun 29, 2014 at 21:40

cvng

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4 Comments

Bergi Over a year ago

No. There's a much simpler solution. Can you spot it?

mietzekotze Over a year ago

return cb(err, decoded), right? :) So that was my mistake? I have to return the function?

cvng Over a year ago

@Bergi It put it in two parts, because you usually wanna do some stuff with results (here decoded) before last return.

Bergi Over a year ago

No. I mean jwt.verify(token, secretToken, cb);, as I had not expected that the OP wants to do some stuff to the results.

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