codex-lv4-may-2025

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Level 3: Create Your First Express Server

1. Create your project structure:
   • Create a src directory
   • Create src/index.js as your main server file

   Show Me: starter Express server code

   // src/index.js
   import express from 'express';
      
   const app = express();
   const port = 3000;
      
   app.get('/', (req, res) => {
     res.send('Hello World!');
   });
      
   app.listen(port, () => {
     console.log(`Server listening on port ${port}`);
   });
   

   See: Express Hello World Example for a minimal Express app example.

Now you’re ready to start building your Express server!

Try It!

Test your server setup:

1. Start the development server:

   npm run dev
   

   • The server should start and display “Server listening on port 3000”
   • Open http://localhost:3000 in your browser
   • You should see “Hello World!” displayed
   • Try making a change to src/index.js (like changing the message) and save—nodemon will automatically restart the server!

2. Stop the server (press Ctrl+C in your terminal)

3. Start the production server:

   npm start
   

   • The server starts the same way, but without auto-restart
   • Make a change to your code and save—notice the server doesn’t restart automatically
   • Stop the server again (Ctrl+C)

💡 Tip: Use npm run dev during development for the auto-restart feature, and npm start when you want to test the production behavior.