JSON response parsing in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to parse JSON response using fetch and extract data.

React Native

fetch('https://api.example.com/data')
  .then(response => response.[1]())
  .then(data => console.log(data))
  .catch(error => console.error(error));

Drag options to blanks, or click blank then click option'

AformData

Btext

Cblob

Djson

Attempts:

3 left

💡 Hint

Common Mistakes

Using response.text() instead of response.json() causes raw text output.

Forgetting to call the method as a function (missing parentheses).

The fetch API response has a json() method to parse the JSON body.

2fill in blank

medium

Complete the code to extract the 'name' property from the parsed JSON object.

React Native

fetch('https://api.example.com/user')
  .then(response => response.json())
  .then(data => {
    const userName = data.[1];
    console.log(userName);
  });

Drag options to blanks, or click blank then click option'

Ausername

Buser

Cname

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong property name that does not exist in the JSON.

Trying to access nested properties without checking the structure.

Assuming the JSON has a 'name' property, access it with data.name.

3fill in blank

hard

Fix the error in accessing nested JSON data inside the response.

React Native

fetch('https://api.example.com/profile')
  .then(response => response.json())
  .then(data => {
    const city = data.address[1]city;
    console.log(city);
  });

Drag options to blanks, or click blank then click option'

A->

B.

C["address"]

D['address']

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' which is not valid in JavaScript.

Using bracket notation incorrectly without quotes.

Use dot notation to access nested properties: data.address.city.

4fill in blank

hard

Fill both blanks to correctly parse JSON and extract the first item from an array.

React Native

fetch('https://api.example.com/items')
  .then(response => response.[1]())
  .then(data => {
    const firstItem = data.[2][0];
    console.log(firstItem);
  });

Drag options to blanks, or click blank then click option'

Ajson

Btext

Citems

Dresults

Attempts:

3 left

💡 Hint

Common Mistakes

Parsing response as text instead of JSON.

Accessing a wrong property name that does not hold the array.

Use response.json() to parse JSON, then access the 'items' array to get the first element.

5fill in blank

hard

Fill all three blanks to parse JSON, extract user info, and check if age is over 18.

React Native

fetch('https://api.example.com/userinfo')
  .then(response => response.[1]())
  .then(data => {
    const user = data.[2];
    if (user.age [3] 18) {
      console.log('Adult user');
    }
  });

Drag options to blanks, or click blank then click option'

Ajson

Bprofile

C>

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Parsing response as text instead of JSON.

Using wrong property name for user data.

Using incorrect comparison operator.

Parse JSON with response.json(), access 'profile' property, and check if age > 18.

Practice

1. What does response.json() do in React Native when fetching data?

easy

A. It displays the JSON data on the screen.

B. It sends data back to the server.

C. It converts the server response into a JavaScript object.

D. It stops the fetch request.

Solution

1. Step 1: Understand the fetch response

   The fetch API returns a response object that contains the raw data from the server.

2. Step 2: Use response.json() to parse data

   The response.json() method reads the raw response and converts it into a usable JavaScript object.

3. Final Answer:

   It converts the server response into a JavaScript object. -> Option C

4. Quick Check:

   response.json() = parse JSON [OK]

Hint: Remember: response.json() parses JSON to object [OK]

Common Mistakes:

• Thinking response.json() sends data to server
• Assuming response.json() displays data directly
• Confusing response.json() with stopping fetch

2. Which of the following is the correct syntax to fetch and parse JSON data in React Native?

easy

A. fetch(url).then(response => response.json())

B. fetch(url).then(response => response.text())

C. fetch(url).json()

D. fetch(url).parseJSON()

Solution

1. Step 1: Recall fetch syntax

   The fetch function returns a promise with a response object.

2. Step 2: Use response.json() to parse JSON

   The correct method to parse JSON from the response is response.json(), which returns a promise with the parsed object.

3. Final Answer:

   fetch(url).then(response => response.json()) -> Option A

4. Quick Check:

   Correct fetch JSON syntax = fetch(url).then(response => response.json()) [OK]

Hint: Use response.json() after fetch to parse JSON [OK]

Common Mistakes:

• Using response.text() instead of response.json()
• Calling json() directly on fetch without then
• Using non-existent parseJSON() method

3. Given the code snippet:

fetch('https://api.example.com/data')
  .then(response => response.json())
  .then(data => console.log(data.name))
  .catch(error => console.error(error));

What will be logged if the JSON response is {"name": "Alice", "age": 25}?

medium

A. "Alice"

B. undefined

C. 25

D. Error

Solution

1. Step 1: Parse JSON response

   The response JSON is parsed into an object: {name: "Alice", age: 25}.

2. Step 2: Access the 'name' property

   The code logs data.name, which is "Alice".

3. Final Answer:

   "Alice" -> Option A

4. Quick Check:

   data.name = "Alice" [OK]

Hint: Access parsed JSON properties directly by name [OK]

Common Mistakes:

• Logging data instead of data.name
• Expecting age instead of name
• Not parsing JSON before accessing properties

4. What is wrong with this React Native fetch code?

fetch('https://api.example.com/data')
  .then(response => response.json)
  .then(data => console.log(data))
  .catch(error => console.error(error));

medium

A. No catch block for errors

B. Missing parentheses after response.json

C. console.log should be console.error

D. fetch URL is incorrect

Solution

1. Step 1: Check response.json usage

   The code uses response.json without parentheses, so it references the function but does not call it.

2. Step 2: Correct function call syntax

   It should be response.json() to actually parse the JSON.

3. Final Answer:

   Missing parentheses after response.json -> Option B

4. Quick Check:

   Call response.json() with () [OK]

Hint: Always call response.json() with parentheses [OK]

Common Mistakes:

• Forgetting parentheses after response.json
• Assuming fetch URL is wrong without checking
• Confusing console.log and console.error usage

5. You receive this JSON response from a server:

{"users": [{"id": 1, "name": "Bob"}, {"id": 2, "name": "Carol"}]}

How do you extract an array of user names in React Native after parsing?

hard

A. data.names

B. data.map(user => user.name)

C. data.users.name

D. data.users.map(user => user.name)

Solution

1. Step 1: Understand JSON structure

   The JSON has a key "users" which is an array of user objects.

2. Step 2: Use map to extract names

   To get all names, use data.users.map(user => user.name) which creates a new array of names.

3. Final Answer:

   data.users.map(user => user.name) -> Option D

4. Quick Check:

   Map over data.users to get names [OK]

Hint: Map over array property to extract values [OK]

Common Mistakes:

• Mapping directly on data instead of data.users
• Trying to access data.users.name which is undefined
• Assuming data.names exists