Question

I am using node-mongodb-native driver. I tried

collection.findOne({email: '[e-mail]'}, function(err, result) {
  if (!result) throw new Error('Record not found!');
});

But the error is caught by mongodb driver and the express server is terminated.

What’s the correct way for this case?

=== Edit===

I have the code below in app.js

app.configure('development', function() {
    app.use(express.errorHandler({dumpExceptions: true, showStack: true}));
});

app.configure('production', function() {
    app.use(express.errorHandler());
});

Related code in node_modules/mongodb/lib/mongodb/connection/server.js

connectionPool.on("message", function(message) {
    try {
        ......
    } catch (err) {
      // Throw error in next tick
      process.nextTick(function() {
        throw err; // <-- here throws an uncaught error
      })
    }      
});

Answer 1

The correct use is not to throw an error, but to pass it to next function. First you define the error handler:

app.error(function (err, req, res, next) {
    res.render('error_page.jade');
})

(What’s this talk about error being depracated? I don’t know anything about that. But even if then you can just use use. The mechanism is still the same.).

Now in your route you pass the error to the handler like this:

function handler(req, res, next) {
    collection.findOne({email: '[e-mail]'}, function(err, result) {
        if (!result) {
            var myerr = new Error('Record not found!');
            return next(myerr); // <---- pass it, not throw it
        }
        res.render('results.jade', { results: result });
    });
};

Make sure that no other code (related to the response) is fired after next(myerr); (that’s why I used return there).

Side note: Errors thrown in asynchronous operations are not handled well by Express (well, actually they somewhat are, but that’s not what you need). This may crash your app. The only way to capture them is by using

process.on('uncaughtException', function(err) {
    // handle it here, log or something
});

but this is a global exception handler, i.e. you cannot use it to send the response to the user.