JSON Introduction

What Is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based format for structured data. It uses key–value pairs and arrays that both humans and programs can read—the default format for most REST APIs.

JSON is text, not a live object:
  Objects  →  { "key": "value" }
  Arrays   →  [1, 2, 3]

Rules: double-quoted keys & strings · no comments · no trailing commas

JS: JSON.parse(text)  ↔  JSON.stringify(obj)

Despite the name, JSON is language-independent. Python, Java, PHP, Go, and many others all have parsers. It looks like a JavaScript object literal, but with stricter rules.

Why Use JSON?

Apps need a shared way to exchange structured data. JSON is compact, readable, and supported almost everywhere.

How JSON Flows in a Web App

Typical path from server to your code:

Your First JSON Object

A simple user record, then parse it in JavaScript:

{
  "name": "John Doe",
  "age": 30,
  "city": "New York"
}

const jsonString = '{"name":"John Doe","age":30,"city":"New York"}';
const data = JSON.parse(jsonString);
console.log(data.name); // John Doe

const text = JSON.stringify(data);
console.log(text);

John Doe
{"name":"John Doe","age":30,"city":"New York"}

How It Works

1. Structure. Curly braces hold key–value pairs; keys and string values use double quotes.

2. Parse. JSON.parse turns the text into a live JavaScript object.

3. Stringify. JSON.stringify turns an object back into JSON text for storage or APIs.

Next, compare formats in JSON vs XML.

JSON vs XML

Both can carry structured data; JSON won most modern APIs:

When to choose which

JSON Data Types

Only these value types are valid in JSON:

Where Is JSON Used?

JSON shows up across modern software:

Key Takeaways