Home/JavaScript Engine Masterclass 2026/

JSON Mastery

Q: Difference between a JS Object and JSON?

Answer: JSON is a text format, while a JS object is a memory data structure. In JSON, keys must be double-quoted strings, and functions are not allowed. JS objects can have keys without quotes (if they're valid identifiers) and can contain functions..

Q: What happens if you try to JSON.stringify an object with functions?

Answer: The functions will be silently removed from the object in the resulting JSON string..

Q: How do you handle circular references in JSON.stringify()?

Answer: JSON.stringify() will throw a TypeError if it encounters a circular reference. You must either sanitize the object or use a library that handles circular structures..

Master this topic with zero to advance depth.

Expert Answer & Key Takeaways

Mastering JSON Mastery is essential for high-fidelity technical architecture and senior engineering roles in 2026.

JavaScript JSON

JSON stands for JavaScript Object Notation. JSON is a lightweight format for storing and transporting data. It is language independent and easy to understand.

1. JSON Syntax Rules

Data is in name/value pairs: "firstName":"John"
Data is separated by commas: "name":"John", "age":30
Curly braces {} hold objects.
Square brackets [] hold arrays.

[!IMPORTANT] In JSON, keys must be strings, written with double quotes: "name": "John".

2. JSON.parse()

A common use of JSON is to read data from a web server and display the data in a web page. Use JSON.parse() to convert a JSON string into a JavaScript object.

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

3. JSON.stringify()

Use JSON.stringify() to convert a JavaScript object into a JSON string.

const obj = {name: "John", age: 30, city: "New York"};
const myJSON = JSON.stringify(obj);
console.log(myJSON); // '{"name":"John","age":30,"city":"New York"}'

4. Storing Data

When storing data, the data has to be a certain format, and regardless of where you choose to store it, text is always one of the legal formats. JSON makes it possible to store JavaScript objects as text.

// Storing data:
const myObj = {name: "John", age: 31, city: "New York"};
const myJSON = JSON.stringify(myObj);
localStorage.setItem("testJSON", myJSON);

// Retrieving data:
const text = localStorage.getItem("testJSON");
const obj = JSON.parse(text);

JSON Mastery

Expert Answer & Key Takeaways

JavaScript JSON

1. JSON Syntax Rules

2. JSON.parse()

3. JSON.stringify()

4. Storing Data

Top Interview Questions

?Interview Question

?Interview Question

?Interview Question

Course4All Engineering Team

Found an issue or have a suggestion?

JSON Mastery

Expert Answer & Key Takeaways

JavaScript JSON

1. JSON Syntax Rules

2. JSON.parse()

3. JSON.stringify()

4. Storing Data

Top Interview Questions

?Interview Question

?Interview Question

?Interview Question

Course4All Engineering Team

Explore More javascript

Proxies & Reflect

Temporal (New)

Typed Arrays

DOM Introduction

Found an issue or have a suggestion?