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Explore how GitHub Copilot Chat can scaffold, debug, and document a Node.js REST API using slash commands and contextual understanding.

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Scaffolding a Node.js REST API

Start by asking Copilot Chat to generate a minimal Express server with an in-memory users database (id, firstName, lastName, email). It instantly produces server.js: 
// server.js
const express = require('express');
const bodyParser = require('body-parser');

const app = express();
const port = 3000;

app.use(bodyParser.json());

let database = [];
let idCounter = 1;

// Retrieve all users
app.get('/users', (req, res) => {
  res.json(database);
});

// Retrieve a user by ID
app.get('/users/:id', (req, res) => {
  const user = database.find(u => u.id === parseInt(req.params.id));
  if (user) {
    res.json(user);
  } else {
    res.status(404).send('User not found');
  }
});

// Create a new user
app.post('/users', (req, res) => {
  const { firstName, lastName, email } = req.body;
  const newUser = { id: idCounter++, firstName, lastName, email };
  database.push(newUser);
  res.status(201).json(newUser);
});

// Update an existing user
app.put('/users/:id', (req, res) => {
  const { firstName, lastName, email } = req.body;
  const user = database.find(u => u.id === parseInt(req.params.id));
  if (user) {
    user.firstName = firstName;
    user.lastName = lastName;
    user.email = email;
    res.json(user);
  } else {
    res.status(404).send('User not found');
  }
});

app.listen(port, () => {
  console.log(`Server running at http://localhost:${port}`);
});

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Using /new to Scaffold Files

Instead of manually writing the code, use the /new slash command to bootstrap an entire project: 
/new create a Node application API
Copilot Chat generates an index.js with a standard Express setup: 
// index.js
const express = require('express');

const app = express();
const port = 3000;

app.use(express.json());

let users = [];

// Create a new user
app.post('/users', (req, res) => {
  const { id, firstName, lastName, email } = req.body;
  const newUser = { id, firstName, lastName, email };
  users.push(newUser);
  res.status(201).json(newUser);
});

// Get all users
app.get('/users', (req, res) => {
  res.json(users);
});

// Get a single user
app.get('/users/:id', (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));
  if (user) {
    res.json(user);
  } else {
    res.status(404).send('User not found');
  }
});

app.listen(port, () => {
  console.log(`Server running at http://localhost:${port}`);
});
You can tailor the /new command with additional options (e.g., include TypeScript or middleware) to fit your project needs.

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Adding package.json and Splitting into app.js

To turn this into a maintainable Node.js application, Copilot Chat introduces a package.json and refactors the server: 
// package.json
{
  "name": "weatherdemo",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "test": "jest"
  },
  "dependencies": {
    "express": "^4.17.1"
  },
  "devDependencies": {
    "jest": "^27.0.6",
    "supertest": "^6.1.3"
  }
}
Now index.js simply starts the server: 
// index.js
const app = require('./app');
const port = 3000;

app.listen(port, () => {
  console.log(`Server is running on http://localhost:${port}`);
});
And app.js holds all request handlers: 
// app.js
const express = require('express');
const app = express();

app.use(express.json());

let users = [];

// Create user
app.post('/users', (req, res) => {
  const { id, firstName, lastName, email } = req.body;
  const newUser = { id, firstName, lastName, email };
  users.push(newUser);
  res.status(201).json(newUser);
});

// List users
app.get('/users', (req, res) => {
  res.json(users);
});

// Get user
app.get('/users/:id', (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));
  if (user) {
    res.json(user);
  } else {
    res.status(404).send('User not found');
  }
});

// Delete user
app.delete('/users/:id', (req, res) => {
  const index = users.findIndex(u => u.id === parseInt(req.params.id));
  if (index !== -1) {
    users.splice(index, 1);
    res.status(204).send();
  } else {
    res.status(404).send('User not found');
  }
});

module.exports = app;

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Generating Tests

Copilot Chat can scaffold a comprehensive test suite with Jest and Supertest: 
// __tests__/app.test.js
const request = require('supertest');
const app = require('../app');

describe('User API', () => {
  it('should create a new user', async () => {
    const res = await request(app)
      .post('/users')
      .send({ id: 1, firstName: 'John', lastName: 'Doe', email: '[email protected]' });
    expect(res.statusCode).toBe(201);
    expect(res.body).toHaveProperty('id', 1);
  });

  it('should retrieve all users', async () => {
    const res = await request(app).get('/users');
    expect(res.statusCode).toBe(200);
    expect(res.body.length).toBeGreaterThan(0);
  });

  it('should retrieve a user by ID', async () => {
    const res = await request(app).get('/users/1');
    expect(res.statusCode).toBe(200);
    expect(res.body).toHaveProperty('id', 1);
  });

  it('should delete a user and return 404 on next fetch', async () => {
    await request(app).delete('/users/1');
    const res = await request(app).get('/users/1');
    expect(res.statusCode).toBe(404);
  });
});

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Installing and Running

  1. Install dependencies: 
    npm install
  2. Start the server: 
    npm start
    You’ll see: 
    > [email protected] start
> node index.js

Server is running on http://localhost:3000
  3. Test your API endpoints:

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Working Set & Context

Copilot Chat leverages your working set—open files, recent edits, tests, and terminal output—to deliver contextual suggestions and reduce manual highlighting.

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Key Slash Commands

CommandDescriptionExample
/newScaffold new files or entire projects/new create a Node.js REST API
/fixApply fixes to selected code or entire fileHighlight code, run /fix
/terminal last commandExplain your last shell command and its output/terminal last command
/terminal selectionAnalyze a selected block of terminal outputHighlight output, run /terminal selection
# (hashtag)Attach context tags like #changes, #codebase, #file selectionUse #changes in your prompt
/helpShow usage tips based on the current editor file/help
/clearClear the current conversation/clear

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Generating Documentation

Easily ask Copilot Chat to generate API docs without manual comments: 
/**
 * @api {get} /users Retrieve all users
 * @apiName GetUsers
 * @apiGroup User
 *
 * @apiSuccess {Object[]} users List of user objects.
 * @apiSuccess {Number} id User’s unique ID.
 * @apiSuccess {String} firstName First name.
 * @apiSuccess {String} lastName Last name.
 * @apiSuccess {String} email Email address.
 *
 * @apiSuccessExample {json} Success-Response:
 *     HTTP/1.1 200 OK
 *     [
 *       { "id": 1, "firstName": "John", "lastName": "Doe", "email": "john.doe@example.com" }
 *     ]
 */
app.get('/users', (req, res) => { … });

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Switching AI Models

You can toggle between backends (e.g., ChatGPT-4, Claude) via the model dropdown in Copilot Chat to find the best fit for your workflow.

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