1. Inspect the project before changing it

Open the project’s package.json. Look for:

• an express entry under dependencies
• a scripts section, especially a start or dev command
• a main field, which may identify the server entry file
• a "type": "module" field

This tells you how the project expects to run. In particular, a project using "type": "module" generally uses import, while a project without it may use require. Match the style already used by the project instead of mixing the two.

If Express is not listed as a dependency, install it from the project folder with:

npm install express

npm install express

Check that package.json now lists Express and that npm completed without an error. Do not create a second project or run initialization commands.

2. Add a deliberate route

Open the existing server entry file. If you are unsure which file it is, use the main field or the project’s documentation rather than guessing a filename.

Find the part that creates the Express application, or add that small piece in the project’s existing style. Your server needs four ideas:

// Use the import style already present in this project.
const express = /* obtain Express */;

const app = express();
const port = /* choose a local port */;

app.get("/", (request, response) => {
  response.send(/* your deliberate welcome message */);
});

app.listen(port, () => {
  console.log(/* a message that includes the port */);
});

// Use the import style already present in this project.
const express = /* obtain Express */;

const app = express();
const port = /* choose a local port */;

app.get("/", (request, response) => {
  response.send(/* your deliberate welcome message */);
});

app.listen(port, () => {
  console.log(/* a message that includes the port */);
});

Adapt the missing parts to the project:

• If the project uses import, use its existing import style.
• Choose a local port such as 3000, unless the project already specifies one.
• Write a message that makes it obvious this is your server, such as a welcome sentence naming the practice project. Do not leave the response as a generic placeholder.
• The / route matters: / is the path the browser requests when you visit the server’s base address.

Save the file.

3. Run the server

Use the start command documented by the project or listed in package.json under scripts. For example, if the project has a "start" script, run that script through npm rather than inventing a different command.

Watch the terminal for the message from your listen callback. It should indicate that the server is listening on the port you selected.

If the process exits immediately, read the first error carefully:

• An import error often means the module style does not match package.json.
• “Cannot find module express” means the dependency is missing or the command was run from the wrong project folder.
• “Address already in use” means another process has claimed that port; stop that process or choose another available port.

4. Test the result in a browser

Open:

http://localhost:YOUR_PORT

http://localhost:YOUR_PORT

Replace YOUR_PORT with the port in your code.

You should see your deliberate welcome message. This is more than a visual check: it confirms the whole request-and-response path worked.

Now make one small change to the message, save the file, and observe what happens:

• If the server process does not restart automatically, stop it and run the project’s command again.
• Refresh the browser.
• Confirm that the new message appears.

That refresh demonstrates an important boundary: changing a source file does not necessarily change the already-running Node process until the project restarts or uses a file-watching tool.