The Complete JSON Guide

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format built on two universal structures: objects (name/value pairs) and arrays (ordered lists). It has become the dominant format for REST APIs, configuration files, and data storage in modern web development.

JSON Syntax Rules

• Keys must be strings in double quotes
• No trailing commas after the last item
• No JavaScript comments (// or /* */)
• Strings use double quotes only — no single quotes
• Supported types: string, number, boolean, null, object, array

Working with JSON in JavaScript

// Parse JSON string → JavaScript object
const obj = JSON.parse('{"name":"Alice","age":30}');

// Convert object → JSON string (indent = 2 spaces)
const json = JSON.stringify(obj, null, 2);

// Safe parsing
try {
  const data = JSON.parse(userInput);
} catch (e) {
  console.error('Invalid JSON:', e.message);
}

Common JSON Errors

• Unexpected token — missing/extra comma, or unquoted key
• Unexpected end of input — unclosed bracket, brace, or string
• Invalid character — single quotes or a comment in the JSON

JSON vs XML

JSON is typically 30–40% more compact than equivalent XML, maps directly to JavaScript objects, and is faster to parse. XML remains preferable for documents requiring namespaces, schemas (XSD), or comments.

Frequently Asked Questions