Working with JSON Data

JSON (JavaScript Object Notation) is a lightweight data format used to store and exchange data between a client and a server.
It is the most common format for APIs and web services.

1. What Is JSON?

JSON represents data as:

• Key–value pairs

• Arrays and objects

• Text-based and language-independent format

Example:

{
  "name": "Alice",
  "age": 25,
  "skills": ["Node.js", "Express"]
}

2. JSON vs JavaScript Objects

3. Parsing and Stringifying JSON

Convert JSON → JavaScript Object

const obj = JSON.parse('{"name":"Bob"}');

Convert JavaScript Object → JSON

const json = JSON.stringify({ name: 'Bob' });

4. Working with JSON in Node.js

Reading JSON from a File

const fs = require('fs');

const data = fs.readFileSync('data.json', 'utf8');
const users = JSON.parse(data);

Writing JSON to a File

const fs = require('fs');

const users = [{ name: 'John', age: 30 }];
fs.writeFileSync('users.json', JSON.stringify(users, null, 2));

✔ null, 2 formats JSON neatly

5. Sending JSON in Express.js

Sending JSON Response

app.get('/user', (req, res) => {
  res.json({ name: 'Alice', age: 25 });
});

Receiving JSON Data

app.use(express.json());

app.post('/user', (req, res) => {
  console.log(req.body);
  res.send('Data received');
});

6. Handling JSON APIs

Typical API flow:

1. Client sends JSON request

2. Server parses JSON body

3. Server processes data

4. Server responds with JSON

7. Common JSON Operations

• Read data

• Update fields

• Add new entries

• Delete entries

Example:

users.push({ name: 'Sam', age: 28 });

8. Error Handling with JSON

try {
  JSON.parse(invalidData);
} catch (err) {
  console.error('Invalid JSON');
}

9. Best Practices

• Always validate incoming JSON

• Use res.json() instead of res.send()

• Format JSON for readability

• Handle parsing errors properly

10. Real-World Use Cases

• REST APIs

• Configuration files

• Data exchange between services

• Frontend–backend communication

11. Summary

• JSON is the standard data format for web apps

• Easily parsed and generated in Node.js

• Express provides built-in JSON handling

• Essential for API development