Node.js (Express) error handling middleware with router

Question

Here\'s my application structure:

- app.js
- routes
---- index.js

The ExpressJS app creates error handlers for development

Answer 1

You can also create a middleware function to handle error in all routes without copying code everywhere, using arrow functions if you like.

1) Create a const function to handle errors.

either:

const handleErrorAsync = func => (req, res, next) => {
    func(req, res, next).catch((error) => next(error));
};

or

const handleErrorAsync = func => async (req, res, next) => {
    try {
        await func(req, res, next);
    } catch (error) {
        next(error);
    }
};

2) In your router use it for every request:

var router = express.Router();

router.get('/req1', handleErrorAsync(async (req, res, next) => {
   let result = await someAsyncFunction1();
   if(result){
       // res.send whatever
   }
}));
router.post('/req2', handleErrorAsync(async (req, res, next) => {
    let result = await someAsyncFunction2(req.body.param1);
    if(result){
        // res.send whatever
    }
}));
router.post('/req3', handleErrorAsync(async (req, res, next) => {
    let result = await someAsyncFunction3(req.body.param1, req.body.param2);
    if(result){
        // res.send whatever
    }
}));

module.exports = router;

3) In your server main app handle error:

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
    app.use(function (err, req, res, next) {
        res.status(err.status || 500);
        res.render('error.ejs', {
            message: err.message,
            error: err
        });
    });
}

// production error handler
// no stacktraces leaked to user
app.use(function (err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
        message: err.message,
        error: {}
    });
});

This way you can reuse the error handling function in any route. Also, if there are any unhandled errors in any of your functions, this will catch them as well.

Try catch error handling taken from Here

Answer 2

You have to pass it to the next callback which is usually the third parameter in the route handler

var router = express.Router();

router.get('/', function (req, res, next) {
    someAsyncFunction(function(err, result) {
        if (err) {
            next(err); // Handle this error
        }
    }
});

module.exports = router;

calling next(err) will allow the error to be caught in a middleware down the chain with the following signature:

app.use(function (err, req, res, next){
    // do something about the err
});

Reference: http://expressjs.com/en/guide/error-handling.html