JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format widely used for transmitting data between servers and web applications. Its simplicity and readability have made it a staple in modern web development. Whether you’re a fresher or an experienced developer, mastering these JSON interview questions will give you an edge in your next technical interview.
📘 What is JSON?
Answer: JSON stands for JavaScript Object Notation. It’s a format for structuring data, making it easy to read and write for humans and simple to parse and generate for machines. JSON is commonly used for storing and transporting data in web applications.
📘 Why is JSON Used?
Answer: JSON is used for:
- Data Interchange: Facilitates the exchange of data between a server and a client.
- Configuration Files: Stores configuration settings in applications.
- APIs: Commonly used in RESTful APIs for data exchange.
- Data Storage: Serves as a lightweight alternative to XML for storing structured data.
Its language-independent nature and compatibility with most programming languages make it a preferred choice for data interchange.
📘 What are the Basics of JSON?
Answer: The basic structure of JSON includes:
- Data is in name/value pairs:
"name": "John" - Data is separated by commas:
"age": 30, "city": "New York" - Curly braces hold objects:
{ "name": "John", "age": 30 } - Square brackets hold arrays:
[ "apple", "banana", "cherry" ]
JSON supports the following data types:
- String
- Number
- Object
- Array
- Boolean
- Null
📘 What are JSON Rules?
Answer: Key rules to follow in JSON:
- Keys must be strings enclosed in double quotes.
- Values must be a valid JSON data type.
- Data is separated by commas.
- Curly braces
{}denote objects. - Square brackets
[]denote arrays.
For example:
{
"name": "Alice",
"age": 25,
"isStudent": false,
"courses": ["Math", "Science"]
}
📘 What are the Keys of a JSON?
Answer: In JSON, keys are strings that identify values within an object. They must be unique within an object and are always enclosed in double quotes. For example:
{
"firstName": "John",
"lastName": "Doe"
}
Here, "firstName" and "lastName" are keys.
🧠 Top JSON Interview Questions and Answers
1. What is the difference between JSON and XML?
Answer:
- Syntax: JSON uses a simpler syntax with fewer characters.
- Data Types: JSON supports arrays and objects; XML does not.
- Readability: JSON is more readable and easier to write.
- Parsing: JSON parsing is faster and requires less processing.
2. How do you parse JSON data in JavaScript?
Answer: Use JSON.parse() to convert a JSON string into a JavaScript object:
const jsonString = '{"name":"John","age":30}';
const obj = JSON.parse(jsonString);
3. How do you convert a JavaScript object to a JSON string?
Answer: Use JSON.stringify():
const obj = { name: "John", age: 30 };
const jsonString = JSON.stringify(obj);
4. Can JSON keys be numbers?
Answer: No, JSON keys must be strings enclosed in double quotes. Numeric keys are not allowed.
5. Is JSON case-sensitive?
Answer: Yes, JSON is case-sensitive. For example, "Name" and "name" are considered different keys.
6. Can comments be used in JSON?
Answer: No, JSON does not support comments. Including comments will result in a parsing error.
7. What is the MIME type for JSON?
Answer: The MIME type for JSON is application/json.
8. How do you handle null values in JSON?
Answer: Use the null value:
{
"middleName": null
}
9. Can JSON contain functions?
Answer: No, JSON cannot contain functions. It is purely a data format.
10. What are some common use cases for JSON?
Answer:
- APIs: Data exchange between client and server.
- Configuration Files: Storing settings.
- Data Storage: Lightweight data storage in NoSQL databases.
- Web Applications: Transferring data asynchronously.
🔍 People Also Ask
❓ Why is JSON used?
JSON is used for data interchange between servers and clients due to its lightweight and easy-to-read format. It’s language-independent and widely supported across platforms.
❓ What are the basics of JSON?
JSON consists of key-value pairs, supports data types like strings, numbers, objects, arrays, booleans, and null, and uses a syntax similar to JavaScript objects.
❓ What are JSON rules?
JSON rules include using double quotes for keys, separating key-value pairs with commas, and enclosing objects in curly braces and arrays in square brackets.
❓ What are the keys of a JSON?
Keys in JSON are strings enclosed in double quotes that uniquely identify values within an object.
🚀 Final Thoughts
Mastering these JSON interview questions will prepare you for technical interviews in web development, backend services, and API integrations. Understanding JSON’s structure, syntax, and use cases is essential for modern developers.