Node.js Express Middleware Not Executing Sequentially with Async Functions
I'm trying to configure Quick question that's been bugging me - I'm having a hard time understanding I'm currently facing an issue where my middleware functions in an Express.js application are not executing in the expected order when using async functions. I have a simple setup where I'm trying to authenticate users before allowing access to certain routes. Here’s a brief overview of my code: In my `app.js` file, I have the following middleware: ```javascript const express = require('express'); const app = express(); const PORT = process.env.PORT || 3000; // Middleware for authentication app.use(async (req, res, next) => { try { // Simulating database call for user authentication const user = await authenticateUser(req.headers.authorization); if (!user) { return res.status(401).json({ message: 'Unauthorized' }); } req.user = user; next(); } catch (error) { console.error('Authentication error:', error); return res.status(500).json({ message: 'Internal Server Error' }); } }); app.get('/protected', (req, res) => { res.json({ message: `Hello ${req.user.name}, you have access to this route!` }); }); app.listen(PORT, () => { console.log(`Server running on http://localhost:${PORT}`); }); ``` The `authenticateUser` function is defined as follows: ```javascript async function authenticateUser(authHeader) { if (!authHeader) return null; // Simulating a delay to mimic database call await new Promise(resolve => setTimeout(resolve, 100)); return { name: 'John Doe' }; // Mock user } ``` When I send a request to the `/protected` route without an `Authorization` header, I expect it to return a `401 Unauthorized` response. However, I am encountering an issue where the middleware seems to skip the `next()` call entirely and instead returns a `500 Internal Server Error` if there's any unhandled rejection or error in the `authenticateUser` function. I’ve also tried adding a catch block to explicitly handle errors in the `authenticateUser` function, but the error still propagates back to my middleware, causing confusion in my response handling. Here’s how I’ve thought to deal with it: ```javascript async function authenticateUser(authHeader) { try { if (!authHeader) throw new Error('No auth header'); await new Promise(resolve => setTimeout(resolve, 100)); return { name: 'John Doe' }; } catch (error) { return null; // Handling error by returning null } } ``` Still, it’s not resolving the issue. I’ve also confirmed that I’m using Node.js version 14.17.0 and Express version 4.17.1. I would appreciate any guidance on properly managing async execution in this middleware scenario to ensure that errors are handled gracefully without affecting the flow of request processing. This is my first time working with Javascript 3.10. The project is a desktop app built with Javascript. Thanks for your help in advance! This is part of a larger microservice I'm building. Has anyone else encountered this? This is my first time working with Javascript 3.10. Any advice would be much appreciated.