JavaScript: JSON (In-Depth)

JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write, and easy for machines to parse and generate. JSON is widely used for data exchange between browsers and servers, especially with APIs.

JSON Structure

• Data is in name/value pairs (like JS objects)
• Keys are always double-quoted strings
• Values can be strings, numbers, objects, arrays, true, false, or null

{
  "name": "Rafi",
  "age": 25,
  "skills": ["JS", "HTML", "CSS"],
  "isActive": true
}
    

Converting JS to JSON

let obj = { a: 1, b: 2 };
let str = JSON.stringify(obj); // '{"a":1,"b":2}'
    

Converting JSON to JS

let s = '{"a":1,"b":2}';
let o = JSON.parse(s); // { a: 1, b: 2 }
    

JSON and APIs

Most web APIs send and receive JSON. Use JSON.stringify() to send, and response.json() or JSON.parse() to receive.

fetch("https://api.example.com/user")
  .then(res => res.json())
  .then(data => console.log(data));
    

Limitations of JSON

• Cannot encode functions, undefined, or special JS types (like Date, Map, Set, etc.)
• All object keys must be strings (no symbols, etc.)

let obj = { a: undefined, b: () => {}, c: 123 };
let s = JSON.stringify(obj); // '{"c":123}'