Express JS - basic

What is Express.js ?

At the time of writing, Express (v4.18.3) is Fast, unopinionated, minimalist web framework for Node.js

Bolierplate code (at the minimum)

Create a folder and initialize a node project (with default values)
```
npm init -y
```
Install the express package and middleware body-parser
```
npm install --save express body-parser
```

Create a file called index.js and copy the following code

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

// Define a route
app.get('/', (req, res) => {
    res.send('Hello, Express!');
});

// Start the server
app.listen(port, () => {
    console.log(`Server is listening at http://localhost:${port}`);
});

Run the server using following command
```
node index.js
```
The server should be started at http://localhost:3000. Upon opening the link, “Hello, Express!” will be served

This is a very minum setup required to start a Express server.

Body Parser middleware

In the above code, body-parser middleware is installed. This is usually required, in case developing an JSON-based API.

So, we can now extend the server code like below, to get users and set (update) a particular user.

const express = require('express');
const bodyParser = require('body-parser');

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

// Body Parser middleware
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());

// Sample data
let users = [
  { id: 1, name: 'John Doe' },
  { id: 2, name: 'Jane Smith' },
  { id: 3, name: 'Bob Johnson' }
];

// GET route to retrieve all users
app.get('/users', (req, res) => {
  res.json(users);
});

// POST route to update user data
app.post('/users/:id', (req, res) => {
  const userId = parseInt(req.params.id);
  const newName = req.body.name;

  const userIndex = users.findIndex(user => user.id === userId);

  if (userIndex !== -1) {
    users[userIndex].name = newName;
    res.json({ message: 'User updated successfully', user: users[userIndex] });
  } else {
    res.status(404).json({ message: 'User not found' });
  }
});

// Start the server
app.listen(port, () => {
  console.log(`Server is listening at http://localhost:${port}`);
});

Test the above code

To get all users, go to the location http://localhost:3000/users
To post (or update) an user, you can simply use any REST Client extensions or if cURL is available, then the following code updates user2
```
curl -X POST http://localhost:3000/users/2 \
-H "Content-Type: application/json" \
-d '{"name": "New User"}'
```

Upon successfull execution, the following result should be shown.

{
    "message":"User updated successfully",
    "user": { "id":2, "name":"New User" }
}