Question

I am working with a partner on a project. He has written a lot of code in Node.js+Express, but we’ve been running into issues with the architecture.

To remedy this, my primary role has been to figure out the best way to architect a Node.js+Express application. I’ve run into two scenarios, dealing with errors, and I’d like some suggestions.

First, how do I capture top-level exceptions? The last thing I want is for a bug to completely kill the node process. I want to continue serving users in the face of any error.

Secondly, some errors are passed back via callbacks (we’re using caolan / async). As part of each route handler, either we render a view (GET), redirect to another route (POST) and we want to redirect to an error screen with a custom error message. How can I make sure to capture this logic in one place?

Answer 1

First, how do I capture top-level exceptions? The last thing I want is for a bug to completely kill the node process. I want to continue serving users in the face of any error.

Edit: I think node’s philosophy in general is that any uncaught exceptions should kill the process, and that you should run your node app under some kind of process monitor with appropriate logging facilities. The following advice is regarding any other errors you might encounter in your express route handlers etc.

Express has a general errorHandler, which should capture all thrown errors as well as everything passed as a parameter to next in your routes/middlewares, and respond with 500 Internal Server Error.

Secondly, some errors are passed back via callbacks (we’re using caolan / async). As part of each route handler, either we render a view (GET), redirect to another route (POST) and we want to redirect to an error screen with a custom error message. How can I make sure to capture this logic in one place?

You could create a custom handleError, which you call in each callback like so:

async.series(..., function(err, results) {
  if(err)
    return handleError(req, res, err);
  // ...
});

Or you could just pass the errors on with next(err) and implement your custom error handler as described here: http://expressjs.com/guide/error-handling.html