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.

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1. What is the purpose of the space parameter in JSON.stringify()?

A) To add extra spacing between keys and values

B) To compress the JSON output

C) To format the output with indentation

D) To add a specific number of spaces to the start of the output

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2. How do you reference the parent key in a deeply nested JSON object?

A) Use key.parent

B) Use parent() function

C) Use a library to navigate JSON paths

D) JSON does not support parent references

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3. How do you specify a format for email validation in JSON Schema?

A) pattern: "/[email]/"

B) type: "email"

C) format: "email"

D) validate: "email"

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

A) [1, 2, , 4]

B) [1, 2, null, 4]

C) Throws a SyntaxError

D) [1, 2, undefined, 4]

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5. What does the package.json file in a Node.js project contain?

A) Metadata about the project, dependencies, and scripts

B) A list of all JavaScript files

C) The project's CSS styles

D) The project's HTML templates

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6. Which messaging protocol often uses JSON for message payloads?

A) POP3

B) SMTP

C) FTP

D) MQTT

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7. How are floating-point numbers represented in JSON?

A) 1.23f

B) 1.23

C) "1.23"

D) float(1.23)

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8. Which of the following JSON strings can be parsed without error?

A) '{"name": John, "age": 30}'

B) '{name: "John", age: 30}'

C) '{name: John, age: 30}'

D) '{"name": "John", "age": 30}'

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

A) .json

B) .txt

C) .js

D) .xml

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10. Which of the following values can be used as JSON keys?

A) Strings only

B) Any data type

C) Strings and numbers

D) Strings and booleans

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11. What is the effect of caching JSON responses?

A) Reduces server processing time for repeated requests

B) Increases JSON size

C) Prevents JSON injection attacks

D) Converts JSON to binary format

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

A) It returns an empty object

B) It converts successfully

C) It skips the circular reference and continues

D) It throws a TypeError

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13. What does the JSON.parse() method do in JavaScript?

A) Validates a JSON string

B) Parses a JSON string into an XML object

C) Converts a JavaScript object into a JSON string

D) Converts a JSON string into a JavaScript object

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14. What does the Content-Type header specify in an API request?

A) The format of the data being sent or expected

B) The size of the request body

C) The status of the response

D) The HTTP method to be used

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

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

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

C) Throws an error

D) {"key1": "value1"}

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16. How do you represent a key-value pair where the value is an array?

A) { "key": [ "value1", "value2" ] }

B) [ { "key": "value1" } ]

C) { "key": "value1", "value2" }

D) { "key": { "value1": "value2" } }

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17. What is the purpose of application/json MIME type?

A) To identify JSON data format

B) To convert JSON to XML

C) To parse JSON

D) To define JSON structure

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

A) Converts to an empty object

B) Returns null

C) Throws a SyntaxError

D) Skips invalid parts

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19. Which JSON data type is used to group key-value pairs?

A) Object

B) Array

C) Number

D) String

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20. How does Firebase use JSON?

A) To define cloud functions

B) For real-time database storage and synchronization

C) To render user interfaces

D) To manage authentication tokens

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

A) Object

B) String

C) Array

D) Null

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22. Can a JSON object have duplicate keys?

A) Only in arrays

B) Only in nested objects

C) Yes

D) No

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23. What does a JSON path debugger do?

A) Validates JSON syntax

B) Beautifies JSON

C) Converts JSON to CSV

D) Extracts specific values from JSON

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24. What happens when you pass a replacer function to JSON.stringify()?

A) It validates the JSON string

B) Throws an error if the function is invalid

C) It ensures all properties are stringified

D) It filters the properties to be included in the JSON string

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25. Which of the following is an invalid JSON structure?

A) { "key": "value", "key": "anotherValue" }

B) { "key": { "nested": { "deep": [1, 2] } } }

C) [ { "key1": "value1" }, { "key2": "value2" } ]

D) { "key": [1, 2, { "nested": "value" }] }

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26. Which keyword is used to specify required fields in a JSON object?

A) mandatory

B) fields

C) required

D) include

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27. Which tool can convert a JSON file into a different format like CSV?

A) Postman

B) jq

C) JSONLint

D) JSON Formatter

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28. What happens when a fetch() request encounters a network error?

A) Throws a TypeError

B) Continues execution without errors

C) Returns undefined

D) Returns an empty object

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29. What is the difference between allOf and oneOf in JSON Schema?

A) allOf is for strings, oneOf is for arrays

B) allOf validates all schemas, oneOf validates only one schema

C) allOf allows duplicates, oneOf does not

D) oneOf requires at least one match, allOf requires none

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30. What is the purpose of the additionalProperties keyword?

A) To specify array constraints

B) To validate nested objects

C) To allow duplicate keys in an object

D) To define extra fields that are allowed in an object

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