What is JSON? Everything You Need to Know

JSON is everywhere. APIs send data in JSON. Configuration files use JSON. If you're a developer, you'll work with JSON daily. Let's understand it completely.

What is JSON?

JSON stands for JavaScript Object Notation. It's a lightweight format for storing and exchanging data. It's easy for humans to read and easy for machines to parse.

{
  "name": "John",
  "age": 25,
  "isActive": true,
  "hobbies": ["reading", "gaming", "coding"]
}

JSON Data Types

• String — Text in double quotes: "hello"
• Number — Integers or decimals: 42, 3.14
• Boolean — True or false: true, false
• Array — Ordered list: [1, 2, 3]
• Object — Key-value pairs: {"key": "value"}
• Null — Empty value: null

JSON vs JavaScript Objects

JSON looks like JavaScript objects, but there are differences:

// JavaScript object (no quotes on keys)
const user = { name: "John", age: 25 };

// JSON (quotes required on keys)
const jsonString = '{"name": "John", "age": 25}';

JSON is a text format. JavaScript objects are in-memory structures. You convert between them using JSON.parse() and JSON.stringify().

Working with JSON in JavaScript

// Parse JSON string to object
const data = JSON.parse('{"name": "John", "age": 25}');

// Convert object to JSON string
const json = JSON.stringify({ name: "John", age: 25 });

// Access JSON data
console.log(data.name); // "John"

JSON in APIs

Most APIs send and receive JSON. When you make a request, the response is usually JSON:

fetch('https://api.example.com/users')
  .then(res => res.json())
  .then(data => {
    console.log(data); // JSON object
  });

JSON Files

JSON files use the .json extension. They're used for configuration, data storage, and more:

{
  "name": "my-project",
  "version": "1.0.0",
  "dependencies": {
    "express": "^4.18.0",
    "react": "^18.0.0"
  }
}

This is a package.json file — every Node.js project has one.

Common Mistakes

• Trailing commas — JSON doesn't allow them
• Single quotes — JSON requires double quotes
• Comments — JSON doesn't support comments
• Undefined — JSON doesn't have undefined, only null