Express middleware

index.js

const express = require('express');
const createHttpError = require('http-errors');

const app = express();

app.get('/foo',
	middlewareOne,
	middlewareTwo,
	fooHandler
);

// should come after all other route handlers
app.use(errorHandler);

app.listen(3000, () => console.log('listening'));

function middlewareOne(req, res, next) {
	console.log('hit middleware one');

	const secretHeader = req.get('x-secret-header');

	if (secretHeader !== 'valid-value') {
		res.status(403).end();
		// important
		return;
	}
	next();
}

function middlewareTwo(req, res, next) {
	console.log('hit middleware two');

	const { id
	} = req.body;

	const isValidId = (id) => typeof id === 'string';

	if (!isValidId(id)) {
		res.status(400).json({
			message: 'bad id'
		});
		// important
		return;
	}
	next();
}

function fooHandler(req, res, next) {
	try {
		// do some logic that might throw
	} catch (error) {
		next(error); // forward error to error handler
	}
}

function errorHandler(err, req, res, next) {
	const httpError = createHttpError(err);
	const { status
	} = httpError;
	res.status(status).json(httpError);
}