JSON as standard format in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JSON parsing code?

Consider this JavaScript code that parses a JSON string and accesses a property.

What will be logged to the console?

Rest API

const jsonString = '{"name": "Alice", "age": 30}';
const obj = JSON.parse(jsonString);
console.log(obj.name);

A Alice

B undefined

C SyntaxError

D null

💡 Hint

Think about what JSON.parse does to a JSON string.

JSON.parse converts a JSON string into a JavaScript object. Accessing obj.name returns the value 'Alice'.

🧠 Conceptual

intermediate

Why is JSON preferred as a standard format in REST APIs?

Which of the following is the main reason JSON is widely used as a standard format in REST APIs?

A It requires special software to read

B It supports complex binary data natively

C It is human-readable and easy to parse by machines

D It is only compatible with JavaScript

💡 Hint

Think about readability and compatibility.

JSON is text-based, easy for humans to read and for machines to parse, making it ideal for data exchange.

🔧 Debug

advanced

What error does this JSON parsing code produce?

What error will this JavaScript code produce when run?

Rest API

const badJson = '{name: "Bob", age: 25}';
const data = JSON.parse(badJson);

A No error, data contains the object

B SyntaxError: Unexpected token n in JSON at position 1

C ReferenceError: badJson is not defined

D TypeError: Cannot read property 'name' of undefined

💡 Hint

Check the JSON string format carefully.

JSON keys must be in double quotes. Missing quotes cause a SyntaxError during parsing.

❓ Predict Output

advanced

What is the output of this REST API JSON response handling code?

Given this JavaScript code snippet that fetches JSON data from an API, what will be logged?

Rest API

async function getUser() {
  const response = await fetch('https://api.example.com/user');
  const data = await response.json();
  console.log(data.active);
}

// Assume the API returns: {"id": 1, "name": "Eve", "active": false}
getUser();

A false

B SyntaxError

C undefined

D true

💡 Hint

Look at the value of the 'active' property in the JSON response.

The API returns active as false, so logging data.active outputs false.

🚀 Application

expert

How many keys are in this JSON object after parsing?

Consider this JSON string and the code that parses it.

How many keys does the resulting object have at the top level?

Rest API

const jsonStr = '{"user": {"id": 10, "name": "Sam"}, "status": "active", "roles": ["admin", "user"]}';
const obj = JSON.parse(jsonStr);
console.log(Object.keys(obj).length);

A 5

B 2

C 4

D 3

💡 Hint

Count only the keys at the top level of the object.

The top-level keys are 'user', 'status', and 'roles', totaling 3 keys.

Practice

1. What is the main reason REST APIs use JSON as their standard format?

easy

A. Because JSON is easy to read and write for both humans and machines

B. Because JSON requires special software to understand

C. Because JSON is a binary format

D. Because JSON only supports numbers

Solution

1. Step 1: Understand JSON format

   JSON is a text-based format that uses simple syntax with objects and arrays.

2. Step 2: Identify why REST APIs prefer JSON

   REST APIs use JSON because it is easy for humans to read and easy for machines to parse.

3. Final Answer:

   Because JSON is easy to read and write for both humans and machines -> Option A

4. Quick Check:

   JSON is text-based and readable [OK]

Hint: JSON is popular because it's simple and readable [OK]

Common Mistakes:

• Thinking JSON is binary
• Believing JSON needs special software
• Assuming JSON only supports numbers

2. Which of the following is the correct JSON syntax for an object with a key "name" and value "Alice"?

easy

A. {"name" = "Alice"}

B. {name: "Alice"}

C. ["name": "Alice"]

D. {"name": "Alice"}

Solution

1. Step 1: Recall JSON object syntax

   JSON objects use curly braces with keys and values as strings, keys must be in double quotes.

2. Step 2: Check each option

   {"name": "Alice"} uses double quotes correctly around key and value, with colon separator.

3. Final Answer:

   {"name": "Alice"} -> Option D

4. Quick Check:

   Keys and strings in double quotes [OK]

Hint: Keys and string values must be in double quotes [OK]

Common Mistakes:

• Omitting quotes around keys
• Using square brackets for objects
• Using equals sign instead of colon

3. Given this JSON response from a REST API:

{"status": "success", "data": [10, 20, 30]}

What is the value of the key "data"?

medium

A. "success"

B. [10, 20, 30]

C. 10

D. {"status": "success"}

Solution

1. Step 1: Identify the key "data" in JSON

   The key "data" holds an array with values 10, 20, and 30.

2. Step 2: Match the value to the options

   [10, 20, 30] correctly shows the array [10, 20, 30].

3. Final Answer:

   [10, 20, 30] -> Option B

4. Quick Check:

   Key "data" = array [10, 20, 30] [OK]

Hint: Look for the key and read its value exactly as shown [OK]

Common Mistakes:

• Confusing key "status" value with "data"
• Picking a single number instead of the array
• Choosing the whole JSON object as value

4. You receive this JSON string from an API:

{"user": "Bob", "age": 25,}

What is wrong with this JSON?

medium

A. Trailing comma after the last item is invalid

B. Keys must be numbers, not strings

C. Values cannot be numbers

D. Missing square brackets around the object

Solution

1. Step 1: Check JSON syntax rules

   JSON objects cannot have a comma after the last key-value pair.

2. Step 2: Identify the error in the string

   The comma after "age": 25 is invalid and causes a syntax error.

3. Final Answer:

   Trailing comma after the last item is invalid -> Option A

4. Quick Check:

   No trailing commas allowed in JSON objects [OK]

Hint: No commas after last item in JSON objects [OK]

Common Mistakes:

• Thinking keys must be numbers
• Believing numbers are invalid values
• Adding brackets incorrectly

5. You want to send a JSON payload to a REST API with user info: name "Eve", age 28, and hobbies as an array of "reading" and "swimming". Which JSON is correct?

hard

A. {"name": "Eve", "age": 28, "hobbies": "reading, swimming"}

B. {"name": Eve, "age": "28", "hobbies": ("reading", "swimming")}

C. {"name": "Eve", "age": 28, "hobbies": ["reading", "swimming"]}

D. {"name": "Eve", "age": 28, "hobbies": {"reading", "swimming"}}

Solution

1. Step 1: Check correct JSON types for each field

   Name is a string, age is a number, hobbies is an array of strings.

2. Step 2: Validate each option's syntax

   {"name": "Eve", "age": 28, "hobbies": ["reading", "swimming"]} correctly uses double quotes for strings, numbers without quotes, and square brackets for array.

3. Final Answer:

   {"name": "Eve", "age": 28, "hobbies": ["reading", "swimming"]} -> Option C

4. Quick Check:

   Strings in quotes, numbers plain, arrays in brackets [OK]

Hint: Use quotes for strings, brackets for arrays, no quotes for numbers [OK]

Common Mistakes:

• Using parentheses instead of brackets for arrays
• Not quoting string values
• Putting numbers in quotes unnecessarily