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

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

B) {"key1": "value1"}

C) Throws an error

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

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2. Can a JSON object have duplicate keys?

A) Yes

B) Only in nested objects

C) No

D) Only in arrays

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3. What does the Content-Security-Policy header do for JSON responses?

A) Specifies how JSON is cached

B) Ensures JSON is minified

C) Restricts where JSON can be loaded from to prevent cross-site scripting (XSS) attacks

D) Defines the format of JSON data

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

A) To define the schema

B) To format query results

C) To handle authentication

D) To manage subscriptions

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

A) Deeply nested objects

B) Flat, simple key-value pairs

C) JSON with comments

D) Objects with arrays

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6. Which of the following is the correct way to represent an empty JSON object?

A) {}

B) []

C) null

D) ""

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7. What does a JSON compressor do?

A) Beautifies JSON

B) Converts JSON to XML

C) Removes unnecessary whitespace for smaller size

D) Validates JSON

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8. Which function can convert an API response from JSON to JavaScript objects?

A) JSON.decode()

B) response.parse()

C) response.json()

D) JSON.stringify()

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9. Which of these is NOT allowed in JSON arrays?

A) Mixed data types

B) Functions as elements

C) Objects as elements

D) Nested arrays

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10. Can JSON keys have spaces?

A) Yes, with quotes

B) No

C) Yes, without quotes

D) Only in arrays

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

A) Combines multiple schemas

B) Validates against one specific type

C) Requires all listed schemas to match

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

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

A) A number

B) An object or array

C) A string

D) A key-value pair

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13. How do you check if a string is valid JSON in JavaScript?

A) Parse it with JSON.parse() inside a try...catch block

B) Use typeof to check its type

C) Use JSON.isValid()

D) Use JSON.check()

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14. Why is it important to remove unused fields from JSON responses?

A) To avoid key duplication

B) To reduce payload size and improve performance

C) To enhance JSON readability

D) To prevent JSON schema validation errors

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15. What does a JSON path debugger do?

A) Beautifies JSON

B) Extracts specific values from JSON

C) Converts JSON to CSV

D) Validates JSON syntax

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

A) The format of the data being sent or expected

B) The status of the response

C) The HTTP method to be used

D) The size of the request body

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17. Which of these web technologies heavily relies on JSON for communication?

A) HTTP/2

B) WebSockets

C) SOAP

D) GraphQL

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18. How do you handle errors in a fetch() request?

A) Using the error property of the response

B) Using fetchError() function

C) Errors cannot be handled in fetch()

D) Using try...catch blocks or then().catch() methods

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19. How is null represented in JSON?

A) NULL

B) (null)

C) "null"

D) null

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

A) Use Object.prototype.toString()

B) Use typeof to check if it is an object

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

D) Use Array.isArray()

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21. What is the output of the code: JSON.stringify({ key: undefined, key2: "value" });

A) {"key": null, "key2": "value"}

B) {"key": "", "key2": "value"}

C) {"key": undefined, "key2": "value"}

D) {"key2": "value"}

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22. Can JSON objects contain duplicate keys?

A) Yes, with an error

B) No

C) Yes, but only for strings

D) Yes, the last key-value pair overrides the previous ones

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

A) Converts to an empty object

B) Skips invalid parts

C) Throws a SyntaxError

D) Returns null

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24. 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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25. What does the enum keyword specify in JSON Schema?

A) The format of a date field

B) A list of allowed values for a property

C) The default value of a property

D) The maximum length of a string

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

A) Use parent() function

B) Use key.parent

C) Use a library to navigate JSON paths

D) JSON does not support parent references

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

A) GET

B) DELETE

C) PUT

D) POST

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28. What does the properties keyword do in JSON Schema?

A) Specifies the data type of an array

B) Defines the maximum number of keys in an object

C) Defines the keys allowed in an object

D) Lists all required fields in an object

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29. What is a common format for API error responses?

A) CSV file

B) Plain text

C) JSON object

D) XML document

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30. What can be the root structure of a JSON document?

A) Only an object

B) A string

C) Either an object or an array

D) Only an array

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