Stop 01 · Internet & Web BasicsTopics · 14/14

JSON

In short

JSON is the language APIs speak. If you can read and write it confidently, you can work with almost any API on the internet.

JavaScript Object Notation — a lightweight, human-readable text format for structuring data, and the de facto standard for API request/response payloads. JSON supports objects, arrays, strings, numbers, booleans, and null, making it easy for frontend and backend systems written in different languages to exchange structured data.

The jaadu hands identical copies of a neat form to three different clerks.

Think of it like this

A form everyone can read

Think of a standard admission form: same fields, same format, so any office can process it. JSON is that standard format for data, and JavaScript, Python, Java and almost every other language can read it.

Watch it happen

Inside a JSON object

student {}

name: "Riya"

age: 19

courses: []

verified: true

"BBA"

"BCA"

1/5The whole thing is one object, wrapped in curly braces.

The big ideas

What you need to know

Keys and values

Data is written as key-value pairs inside curly braces. Keys must be in double quotes.

Six types only

Strings, numbers, true or false, null, arrays and objects. No functions, dates or undefined.

Convert both ways

JSON.stringify turns an object into a JSON string. JSON.parse turns the string back into an object.

Strict rules

No trailing commas, no comments and no single quotes. One small slip and parsing fails.

See it in code

Walk through the code

1const text = '{"name":"Riya","age":19,"courses":["BBA","BCA"],"verified":true}';2 3const student = JSON.parse(text);   // string -> object4console.log(student.courses[0]);    // "BBA"5 6student.age = 20;7const pretty = JSON.stringify(student, null, 2); // object -> readable string

1/3This is JSON as it arrives from an API: just one long string.

The extra arguments in JSON.stringify(student, null, 2) indent the output by 2 spaces, which makes it much easier to read while debugging.

Save yourself the pain

Common mistakes

Oops

Leaving a trailing comma after the last item.

Do this instead

Remove it. JSON.parse throws on {"a": 1,} even though JavaScript objects allow it.

Oops

Expecting dates to come back as Date objects.

Do this instead

JSON stores dates as strings. Turn them back with new Date(value) after parsing.

Oops

Calling JSON.parse on an API response without any error handling.

Do this instead

Wrap it in try/catch so one bad response doesn't crash your app.

Your mission

Fix the broken JSON

~10 min

Quick check

Which of these is valid JSON?

Go deeper

1Practice converting objects to JSON with `JSON.stringify` and back with `JSON.parse`. Test it with at least one normal case and one edge case so you can explain the behavior confidently.
2Inspect a real API response's JSON structure in DevTools. Validate your understanding by applying it in a small practical example.
3Learn valid JSON syntax rules (double quotes, no trailing commas, no comments).