JSON (JavaScript Object Notation)

JSON is a lightweight text format used to exchange structured data between web pages, APIs, and many programming languages.

Basic JSON structures

{
  "name": "Aki",
  "tags": ["web", "beginner"],
  "active": true
}

JSON uses double-quoted property names and values such as strings, numbers, booleans, arrays, objects, or null. It does not contain JavaScript comments or functions.

Using JSON in JavaScript

const text = '{"name":"Aki"}';
const data = JSON.parse(text);
console.log(data.name);

const output = JSON.stringify(data);

JSON.parse() converts JSON text into a JavaScript value. JSON.stringify() converts a JavaScript value into JSON text for storage or transmission.

Safety points

• Validate data received from an API before relying on its shape.
• Use textContent when displaying untrusted values instead of inserting them as HTML.
• JSON is data, not executable code; do not evaluate it with eval().