500 error handler ignored, but exception is caught in process.on('uncaughtException')

[binarykitchen]

Hello guys

I've googled everywhere about my problem without success so I'm trying here to get some help.

In my code, express does not show the 500 error page when an error happens but is logged within process.on('uncaughtException').

Here are the relevant parts of my code:

// near top of server.js
process.on('uncaughtException', function (err) {
    console.error(err);
});

..

// further down in the middle ...
app.configure(function() {
    ...
    app.use(function(err, req, res, next) {
        res.status(err.status || 500);
        res.render('500', { ...}
        );
    });
});

...
require('./routes/clean')(app);

Then somewhere in the route /clean an error is thrown and caught in process.on('uncaughtException') but is never rendered as 500 within express. Why?

[tj]

you have to delegate errors with next(err) in async callbacks, for example:

db.find(id, function(err){
  if (err) throw err;
})

cannot be caught by express, while the following can be:

db.find(id, function(err){
  if (err) return next(err);
})

so something must be throwing instead of delegating

[binarykitchen]

ah, thanks! this is very important information. can you add this somewhere in the guide? http://expressjs.com/guide.html

one last question: what if I'm creating new exceptions inside async callbacks?

like this:

throw new Exception('errrrrror');

should I use

next(new Exception('errrrrror'));

instead?

[binarykitchen]

and um, does this rule apply to all async callbacks or only those within express routes?

for example async callbacks within socket.io?

[tj]

yup it applies to all of node really, one of node's major codesmells

[binarykitchen]

all of node? ouch!

is there an ongoing discussion somewhere else about this smell?