JSON (JavaScript Object Notation) is a lightweight data format used to store and exchange data between a server and a client (for example, between a web browser and a web server).

It’s easy for humans to read and write, and easy for machines to parse and generate.

🧠 Why Use JSON?

• ✅ Simpler and lighter than XML
• ✅ Widely used in APIs and web services
• ✅ Supported by almost all modern programming languages
• ✅ Easy to convert between JSON and data structures like objects, arrays, or dictionaries

🧱 Basic Structure of JSON

JSON data is written as key–value pairs, similar to JavaScript objects.

{
  "name": "Raj",
  "age": 25,
  "isStudent": true,
  "skills": ["HTML", "CSS", "JavaScript"],
  "address": {
    "city": "Mumbai",
    "country": "India"
  }
}

🔍 Explanation:

• { } → Represents a JSON object
• [ ] → Represents a JSON array
• "key": "value" → Each key is a string, and each value can be:
  • A string ("Raj")
  • A number (25)
  • A boolean (true or false)
  • An array (["HTML", "CSS"])
  • Another object ({"city": "Mumbai"})
  • null

🧾 JSON Data Types

Type	Example
String	"Hello"
Number	100, 12.5
Boolean	true, false
Array	["red", "green", "blue"]
Object	{"name": "Raj", "age": 25}
Null	null

⚙️ JSON in JavaScript

Converting a JavaScript Object → JSON string

const user = { name: "Raj", age: 25 };
const jsonString = JSON.stringify(user);
console.log(jsonString);
// Output: {"name":"Raj","age":25}

Converting a JSON string → JavaScript Object

const jsonData = '{"name": "Raj", "age": 25}';
const obj = JSON.parse(jsonData);
console.log(obj.name);
// Output: Raj

🌐 Where JSON is Commonly Used

• APIs (e.g., fetching data from web servers)
• Configuration files (e.g., package.json in Node.js)
• Data storage in NoSQL databases (like MongoDB)
• Web applications for client-server communication

⚠️ JSON Rules

1. Keys must be strings (in double quotes)
2. Values can’t include functions or comments
3. JSON is case-sensitive
4. Commas separate pairs, but no trailing comma

✅ Correct:

{ "name": "Raj", "age": 25 }

❌ Incorrect:

{ name: "Raj", age: 25, }