JSON: The Complete Guide for Developers

What is JSON?

JSON (JavaScript Object Notation) is a lightweight data interchange format. It's easy for humans to read and write, and easy for machines to parse and generate.

JSON Syntax

{
  "name": "John Doe",
  "age": 30,
  "isActive": true,
  "email": null,
  "hobbies": ["reading", "coding", "gaming"],
  "address": {
    "street": "123 Main St",
    "city": "New York"
  }
}

Data Types

Common Mistakes

// ❌ Wrong: Single quotes
{'name': 'John'}
// ✅ Correct: Double quotes
{"name": "John"}
// ❌ Wrong: Trailing comma
{"name": "John",}
// ✅ Correct: No trailing comma
{"name": "John"}
// ❌ Wrong: Comments
{
  "name": "John" // this is a comment
}
// ✅ JSON doesn't support comments
{"name": "John"}

JSON vs JavaScript Objects

// JavaScript object (more flexible)
const jsObj = {
  name: 'John',           // Unquoted keys OK
  'full-name': 'John Doe', // Quoted keys OK
  greet() { },            // Methods allowed
};
// JSON (stricter)
const json = {
  "name": "John",         // Keys must be quoted
  "full-name": "John Doe" // Always double quotes
  // No methods, no functions
};