ExpressJS middleware that also catches errors? - node.js

Question

I'm writing middleware that I'm applying at the route level, like so:
router.get('/foo', myMiddleware, (req, res) => { ... });
so I can do some stuff with the request. But I also need to catch errors to do some special handling. I know I can add a handler afterwards like this:
... (req, res) => { ... }, myErrorHandler);
and it'll get called just fine.
But my question is, is there any way to have a single piece of middleware that can do all of this so I don't need two points of integration? I tried calling req.on('error', (err) => { ... }) within my middleware but it never seems to be called.

Answer 1

Express comes with a built-in error handler that takes care of any errors that might be encountered in the app. This default error-handling middleware function is added at the end of the middleware function stack.
// Router
router.get('/foo', myMiddleware, (req, res) => { ... });
// Router Error Handler
router.use(function (err, req, res, next) {
});

Answer 2

I ended up solving this by writing a helper function that wraps the actual handler. It looks like this:
function checkPage(handler: express.RequestHandler) {
return async (req: express.Request, res: express.Response, next: express.NextFunction) => {
let _write = res.write;
res.write = chunk => {
if (req.query.verbose) {
return _write.call(res, `<p>${chunk}</p>`);
} else {
return true;
}
}
try {
await handler(req, res, next);
res.write('<hr/><p style="color:green;"><b>happy</b></p>');
} catch (err) {
res.write(`<p style="color:red;">${err}</p>`);
res.write('<hr/><p style="color:red;"><b>SAD!</b></p>')
}
res.end();
}
}
Then in my route handler, I just use it like so:
router.get('/foo', checkPage(async (req, res, next) => {
...
res.write('stuff');
...
}));