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 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