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

Space play ←→ step click any line
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.

Related explainers

rust 
use axum::{
    http::StatusCode,
    response::IntoResponse,
    routing::get,

Serving an SPA and API with Axum

routing static-files spa-fallback
Intermediate 7 steps
go 
func RecoveryHandler(logger *zap.Logger) gin.HandlerFunc {
	return gin.CustomRecovery(func(c *gin.Context, recovered any) {
		var brokenPipe bool
		if ne, ok := recovered.(*net.OpError); ok {

A panic-recovery middleware in Gin

middleware panic-recovery structured-logging
Intermediate 6 steps
javascript 
const STORAGE_KEY = "app_state";
const CURRENT_VERSION = 3;
 
const migrations = {

Versioned state migrations in localStorage

migrations persistence versioning
Intermediate 9 steps
python 
from flask import Blueprint, jsonify, request, abort
 
from .models import Article, db
from .schemas import article_schema, articles_schema

Building a REST articles API with Flask Blueprints

rest-api blueprints serialization
Intermediate 7 steps
java 
@RestController
@RequestMapping("/api/users")
public class UserController {
 

Bean Validation in a Spring REST controller

validation rest-api exception-handling
Intermediate 9 steps
go 
package server
 
import (
	"context"

Composing HTTP middleware in Go

middleware http-handlers closures
Intermediate 8 steps

Share this explainer

Here's the card — post it anywhere.

Async error handling in Express routes — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code