how to stop or exit on error with NodeJs

Question

I try to understand how I can stop or exit on error in a Nodejs route. In the code below, I check if header UID is sent and if the fiels group is also sent.

The problem is that nodejs continues to execute the rest of the code even if I use res.end () + return; I wish that Node Js stop everything when I display an error. Perhaps because I do not know much in Node Js I myself take it badly and I have to work otherwise. Can you explain to me and give me an example of how I should do?

var uid;
var group;

if (typeof req.headers['uid'] == 'undefined' || req.headers['uid'] == '') {
    res.status(404);
    res.json('user_id not set');
    res.end();
    return;
}
else
{
    uid = req.headers['uid'];

    User.find({_id:uid}).exec(function(err, data)
    {
        if(err){
            res.status(404);
            res.json('user not found');
            res.end();
            return;
         }
    });
}

if (typeof req.body.group == 'undefined' || req.body.group == '') {
    res.status(500);
    res.json('group not defined');
    res.end();
    return;
}
else
{
    group = req.body.group;
}

@thefourtheye In the code above if the UID is nots sent and GROUP is not sent, i get error : can't set header after they are sent. Of course, Node Js check is user is not found and NOT STOP on the first error ... nodeJs continue to the next error and cause the header error : can't set header after they are already sent. — Pixelight
– Pixelight, Commented Jun 19, 2015 at 8:48
The UID check is happening asynchronously. But the group not defined happens before that. — thefourtheye
– thefourtheye, Commented Jun 19, 2015 at 8:52

jfriend00 · Accepted Answer · 2015-06-19 08:53:18Z

1

it is unclear exactly what you mean by "node js stop everything". If you want to stop the entire nodejs process, you can use process.exit().

If you're trying to keep some code after your error from executing and your error occurs in an async callback, then you can't do that. The other code has already executed.

If you want to serialize asynchronous operations so that you complete one async operation BEFORE you decide whether to start the next operation, then you will need to code that differently. You will need to execute the second block of code from within the completion callback of the first async operation.

One aspect of your code that you may not understand is that this block is asynchronous:

User.find({_id:uid}).exec(function(err, data)
{
    if(err){
        res.status(404);
        res.json('user not found');
        res.end();
        return;
     }
});

The callback you pass to .exec() is called sometime LATER. Meanwhile, the rest of your JS has already executed. In addition, when you do a return from within that callback that doesn't return from your outer function, it only returns from that callback function back into the bowels of .exec(). It stops any more of the callback from executing, but has no effect at all on the outer function because that outer function.

So, if you want the .find() operation to finish before you execute the rest of your code in that function, you have to put that code inside the callback function.

edited Jun 19, 2015 at 8:53

answered Jun 19, 2015 at 8:47

jfriend00

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1 Comment

Pixelight Over a year ago

I don't want to stop the entire Node process but just exit on error. In PHP i make : return 'error'; for example and the rest of the code is not executed time that the error is not resolved.

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