JSON Quiz Test Online (30 random Questions) 2026

This quick 30-minute challenge consists of 30 random multiple-choice questions designed to test your knowledge across various JSON topics, including the introduction to JSON, JSON syntax and basics, data types, operations in JavaScript, APIs and JSON, advanced structures, JSON Schema, tools and debugging, as well as performance and security considerations. Whether you’re new to JSON or looking to refine your skills, this quiz will enhance your understanding of JSON’s role in modern web development.

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30 Minutes JSON Quiz Test Online

Welcome to the JSON Quiz! This quick 30-minute challenge consists of 30 random multiple-choice questions designed to test your knowledge across various JSON topics, including the introduction to JSON, JSON syntax and basics, data types, operations in JavaScript, APIs and JSON, advanced structures, JSON Schema, tools and debugging, as well as performance and security considerations. Whether you're new to JSON or looking to refine your skills, this quiz will enhance your understanding of JSON's role in modern web development.

1 / 30

1. What is the purpose of the dependencies keyword in JSON Schema?

A) To define type constraints

B) To validate nested objects

C) To define key dependencies

D) To specify default values

2 / 30

2. Which of these is a valid boolean value in JSON?

A) true

B) TRUE

C) True

D) "true"

3 / 30

3. What will JSON.stringify({ key: undefined }) return?

A) {"key": null}

B) {"key": "undefined"}

C) {}

D) Throws an error

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4. What happens when you use JSON.stringify() on an object with a circular reference?

A) It ignores the circular reference

B) It throws a syntax error

C) It converts the object to a string successfully

D) It throws a TypeError

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5. What is the root element of a JSON document?

A) An object or array

B) A key-value pair

C) A number

D) A string

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6. How do you check if a given JavaScript object is a valid JSON object?

A) Convert it to a string using JSON.stringify() and back using JSON.parse()

B) Use Object.prototype.toString()

C) Use Array.isArray()

D) Use typeof to check if it is an object

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7. Which of the following is NOT a valid JSON key?

A) "name!"

B) name

C) "123name"

D) "_name"

8 / 30

8. Which of the following best describes JSON?

A) A database system

B) A lightweight data format

C) A programming language

D) A markup language like XML

9 / 30

9. Which browser's developer tools are commonly used to debug JSON in web applications?

A) Google Chrome

B) Safari

C) Internet Explorer

D) Firefox

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10. What happens if a JSON object has circular references when using JSON.stringify()?

A) It skips the circular reference and continues

B) It throws a TypeError

C) It converts successfully

D) It returns an empty object

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11. How are elements in a JSON array separated?

A) Dots

B) Semicolons

C) Commas

D) Colons

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12. What is the output of JSON.parse('[1, 2, , 4]')?

A) [1, 2, undefined, 4]

B) [1, 2, , 4]

C) [1, 2, null, 4]

D) Throws a SyntaxError

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13. How is null represented in JSON?

A) null

B) NULL

C) (null)

D) "null"

14 / 30

14. What will be the output of the code: JSON.stringify({ key1: "value1", key2: function() { return "value2"; } });

A) {"key1": "value1", "key2": null}

B) {"key1": "value1", "key2": "value2"}

C) Throws an error

D) {"key1": "value1"}

15 / 30

15. How do you access the name of the first employee in the JSON structure { "department": { "employees": [ { "name": "John" }, { "name": "Alice" } ] } }?

A) employees[0].name

B) department[employees][name]

C) department.employees[0].name

D) department.employees[1].name

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16. Which of the following is NOT a JSON data type?

A) String

B) Null

C) Date

D) Boolean

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17. Which of the following is true about JSON numbers?

A) They must include a decimal point

B) They must be enclosed in double quotes

C) They support both integers and floats

D) They cannot be negative

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18. What does the oneOf keyword do in JSON Schema?

A) Requires all listed schemas to match

B) Validates against one specific type

C) Combines multiple schemas

D) Ensures that the data matches exactly one of the specified schemas

19 / 30

19. Which HTTP method is typically used for sending data to an API?

A) POST

B) DELETE

C) OPTIONS

D) GET

20 / 30

20. In which cloud service is JSON commonly used for defining infrastructure as code?

A) Firebase

B) Microsoft Azure

C) DigitalOcean

D) Amazon Web Services (AWS) CloudFormation

21 / 30

21. How do you identify invalid JSON in a web application?

A) All of the above

B) Use a linter or formatter tool

C) Use the browser's developer tools

D) Log errors in the console

22 / 30

22. What happens when you use JSON.parse() on an invalid JSON string?

A) Skips invalid parts

B) Returns null

C) Throws a SyntaxError

D) Converts to an empty object

23 / 30

23. Which HTTP method is commonly used to fetch JSON data from an API?

A) POST

B) GET

C) DELETE

D) PUT

24 / 30

24. Which character is used to enclose a JSON array?

A) <>

B) []

C) {}

D) ()

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25. What is the maximum depth for nesting in JSON?

A) 5 levels

B) 10 levels

C) Depends on the programming language and environment

D) Unlimited

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26. What data type is represented by {} in JSON?

A) Null

B) String

C) Array

D) Object

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27. What is the primary role of JSON in GraphQL APIs?

A) To handle authentication

B) To format query results

C) To define the schema

D) To manage subscriptions

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28. What happens when duplicate keys are present in a JSON object?

A) The first key-value pair is ignored

B) Both key-value pairs are stored

C) The last key-value pair overrides the previous ones

D) An error is thrown

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29. Which type of JSON structure is most efficient for transmitting data?

A) JSON with comments

B) Objects with arrays

C) Deeply nested objects

D) Flat, simple key-value pairs

30 / 30

30. What is the typical file extension for JSON files?

A) .xml

B) .js

C) .json

D) .txt

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