JSON Fundamentals, Exams of Programming Languages

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Full Stack JavaScript

JSON

Knowledge Assessment

Q & S

1. Which of the following JSON structures is valid? a) {"name":'John', "age":30} b) {'name':'John', 'age':30} c) {"name":"John", "age":30} d) {name:"John", age:30}

Answer: c

Rationale: JSON requires double quotes for both keys and string values. Option c) follows this format correctly.

2. What will be the result of the following JSON operation in JavaScript?

   var jsonString = '{"name": "Alice", "active": true}'; var obj = JSON.parse(jsonString); console.log(obj.active); 

   a) "true" b) true c) undefined

Answer: a

Rationale: The correct way to add a new key-value pair is using dot notation or array-like notation with the assignment operator (=).

5. Which of the following correctly describes the flexibility of JSON? a) JSON supports comments. b) JSON allows functions to be embedded. c) JSON is strictly for structured data without support for functions or comments. d) JSON supports infinite precision numbers.

Answer: c

Rationale: JSON is designed for structured data and does not support functions or comments. It has limitations in terms of number precision as per IEEE 754 standards.

Fill-in-the-Blank Questions

6. _______ is a method for transforming complex or circular JavaScript objects into JSON format.

Answer: JSON.stringify()

Rationale: JSON.stringify() converts JavaScript objects to a JSON string.

7. To prevent the issue of JSON hijacking, it is recommended to set the content-type of JSON responses to _______ or prefix the response with _______.

Answer: application/json, while(1);

Rationale: Setting the content-type correctly or prefixing responses prevents JSON hijacking.

8. In JSON, arrays are represented using _______, and they are capable of holding multiple types of data including strings, numbers, objects, arrays, and _______.

Answer: [], boolean values

Rationale: Arrays use square brackets and can hold various types of data.

9. When parsing JSON in JavaScript, errors are caught using _______.

Answer: try...catch block

Rationale: The try...catch block is used to handle errors that may occur during JSON.parse().

Answer: False

Rationale: JSON does not have a native date type; dates are typically represented as strings.

14. True or False: JSON does not allow trailing commas after the last value in an array or object.

Answer: True

Rationale: JSON follows a strict syntax that disallows trailing commas.

15. True or False: JSON's flexibility makes it a good option for defining APIs, as it can be extended to include functions.

Answer: False

Rationale: JSON cannot include functions, making it unsuitable for scenarios requiring executable code. It is primarily used for data representation.

Multiple Choice Questions (Advanced)

16. What does this JavaScript code snippet output?

    const data = {a: 'apple', b: 'banana'}; 

console.log(JSON.stringify(data, ['a']));

a) `{"a":"apple"}` b) `{a: "apple"}` c) `{"a":"apple","b":"banana"}` d) `{}` ## Answer: a Rationale: The second parameter of `JSON.stringify()` allows for a whitelist of properties to include in the JSON string. 17. Which statement is true about deeply nested JSON objects and circular references in JavaScript? a) They can always be serialized with JSON.stringify(). b) They cannot be serialized at all. c) They can be handled using a replacer function in JSON.stringify(). d) They automatically resolve during serialization. ## Answer: c Rationale: The `JSON.stringify()` method can take a `replacer` function to handle and potentially omit circular references. ### Fill-in-the-Blank (Advanced) B) text/json C) application/x-json D) text/javascript ## Correct Answer: A) application/json Rationale: The official MIME type for JSON is application/json, which is necessary for proper JSON data interchange. 2. True/False: JSON keys can be non-string data types. ## Correct Answer: False Rationale: In JSON, keys must always be strings enclosed in double quotes. 3. Fill-in-the-blank: In JSON, the _______ data type is used to store simple values like strings, numbers, and Booleans. ## Correct Answer: scalar Rationale: Scalar data types in JSON are used to represent simple data types that are not objects or arrays. 4. Multiple Choice: Which of the following is not a valid JSON value? A) "Hello, World!" B) null C) undefined D) 42 ## Correct Answer: C) undefined Rationale: undefined is not a valid JSON value; JSON only supports null for representing non-values. 5. True/False: JSON supports comments within the data format. ## Correct Answer: False Rationale: JSON does not support comments. Adding comments to a JSON file will invalidate the JSON format. 6. Fill-in-the-blank: To ensure a JSON file is properly formatted, it should be validated against a _______. ## Correct Answer: schema Rationale: A JSON schema defines the structure and rules for a JSON file, ensuring it is correctly formatted. 7. Multiple Choice: What does JSONP stand for? A) JSON Parsing B) JSON Programming C) JSON with Padding D) JSON Printing ## Correct Answer: C) JSON with Padding Rationale: JSONP (JSON with Padding) is a method used to request data from a server residing in a different domain than the client. Rationale: A single string, when properly quoted, is a valid JSON text. 12. Fill-in-the-blank: The process of converting a JavaScript object into a JSON string is known as _______. ## Correct Answer: serialization Rationale: Serialization is the process of converting an object into a format that can be easily shared or stored, such as a JSON string. 13. Multiple Choice: Which of the following characters must be escaped in JSON strings? A)! B) $ C) " D) % ## Correct Answer: C) " Rationale: In JSON, certain characters like the double quote must be escaped to be correctly represented within strings. 14. True/False: JSON can represent date/time data directly as a data type. ## Correct Answer: False Rationale: JSON does not have a date/time data type. Dates are usually represented as strings or numbers in JSON. 15. Fill-in-the-blank: A common use of JSON is to transmit data between a server and a web _______. ## Correct Answer: application Rationale: JSON is widely used for transmitting data between a server and a web application as part of the AJAX technology stack. Multiple Choice: a. What does JSON stand for? A. JavaScript Object Notation B. Java Symbolic Object Notation C. JavaScript Object Navigation D. Java Syntax Object Notation ## Correct Answer: A. JavaScript Object Notation Rationale: JSON stands for JavaScript Object Notation and is a lightweight data interchange format inspired by JavaScript object literal syntax. Fill-in-the-Blank: a. In JSON, data is stored in key-value pairs enclosed in __. ## Correct Answer: curly braces {} Fill-in-the-Blank: a. To represent an array in JSON, the values are enclosed in __. ## Correct Answer: square brackets [] Rationale: Arrays in JSON are represented by enclosing the values in square brackets []. True/False: a. JSON supports nested objects. ## Correct Answer: True Rationale: JSON allows for nested objects where objects can contain other objects as values. Multiple Choice: a. Which method is used to convert a JSON string to a JavaScript object? A. JSON.parse() B. JSON.stringify() C. JSON.convert() D. JSON.object() ## Correct Answer: A. JSON.parse() Rationale: JSON.parse() is used to parse a JSON string and convert it into a JavaScript object. Fill-in-the-Blank: a. JSON data is often transferred between a server and a client using __. ## Correct Answer: HTTP requests Rationale: JSON data is commonly transferred between a server and a client using HTTP requests. True/False: a. JSON supports comments like JavaScript. ## Correct Answer: False Rationale: JSON does not support comments, unlike JavaScript. Multiple Choice: a. Which character is used to separate key and value in a JSON object? Rationale: JSON does not have built-in support for data types such as date and time. Multiple Choice: a. Which method is used to convert a JavaScript object to a JSON string? A. JSON.stringify() B. JSON.objectify() C. JSON.convertToString() D. JSON.string() ## Correct Answer: A. JSON.stringify() Rationale: JSON.stringify() is used to convert a JavaScript object to a JSON string. Fill-in-the-Blank: a. JSON arrays can contain __. ## Correct Answer: a mix of data types Rationale: JSON arrays can contain a mix of data types including strings, numbers, objects, and arrays. True/False: a. JSON is human-readable and easy to write. ## Correct Answer: True Rationale: JSON is designed to be human-readable and easy to write, making it popular for data interchange.