javascript 37 lines · 7 steps

Async error handling in Express routes

A small wrapper forwards rejected promises to Express's error middleware so async route handlers stay clean.

Explained by highlit
Express Intermediate async-await error-handling middleware higher-order-functions rest-api
1const asyncHandler = (fn) => (req, res, next) => {
2 Promise.resolve(fn(req, res, next)).catch(next);
3};
4 
5const router = require('express').Router();
6const { User, Order } = require('../models');
7const { NotFoundError } = require('../errors');
8 
9router.get('/users/:id/orders', asyncHandler(async (req, res) => {
10 const user = await User.findByPk(req.params.id);
11 if (!user) {
12 throw new NotFoundError(`User ${req.params.id} not found`);
13 }
14 
15 const orders = await Order.findAll({
16 where: { userId: user.id, status: req.query.status ?? 'active' },
17 order: [['createdAt', 'DESC']],
18 limit: 50,
19 });
20 
21 res.json({
22 user: { id: user.id, email: user.email },
23 orders: orders.map((o) => o.toJSON()),
24 });
25}));
26 
27router.post('/users/:id/orders', asyncHandler(async (req, res) => {
28 const order = await Order.create({
29 userId: req.params.id,
30 items: req.body.items,
31 total: req.body.total,
32 });
33 
34 res.status(201).json(order);
35}));
36 
37module.exports = router;
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Express doesn't catch rejected promises from async handlers, so an unhandled rejection silently hangs the request unless you forward it to next.
  2. 2A tiny higher-order wrapper removes repetitive try/catch from every route while centralizing error handling.
  3. 3Throwing typed errors inside handlers lets one error middleware translate them into consistent HTTP responses.

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