Why conditional rendering is needed in React - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to render a message only if the user is logged in.

React

function Greeting({ isLoggedIn }) {
  return (
    <div>
      {isLoggedIn && [1]
    </div>
  );
}

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

A<p>Goodbye!</p>

B<p>Welcome back!</p>

C<p>Please sign up.</p>

D<p>Loading...</p>

Attempts:

3 left

💡 Hint

Common Mistakes

Using a message that does not relate to the logged-in state.

Rendering the message regardless of the condition.

Using isLoggedIn && <p>Welcome back!</p> shows the message only when isLoggedIn is true.

2fill in blank

medium

Complete the code to show 'Loading...' text while data is being fetched.

React

function DataLoader({ isLoading }) {
  return (
    <div>
      {isLoading ? [1] : <p>Data loaded</p>}
    </div>
  );
}

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

A<p>Error occurred</p>

B<p>No data</p>

C<p>Loading...</p>

D<p>Ready</p>

Attempts:

3 left

💡 Hint

Common Mistakes

Showing the loaded message even when loading.

Using incorrect JSX inside the ternary.

The ternary operator shows <p>Loading...</p> when isLoading is true, otherwise shows 'Data loaded'.

3fill in blank

hard

Fix the error in the code to conditionally render a button only if the user is an admin.

React

function AdminButton({ isAdmin }) {
  return (
    <div>
      {isAdmin && [1]
    </div>
  );
}

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

A<button>Delete User

Bbutton>Delete User</button>

C<button>Delete User</button

D<button>Delete User</button>

Attempts:

3 left

💡 Hint

Common Mistakes

Missing the opening or closing tag in JSX.

Using incomplete HTML tags inside JSX.

The correct JSX for a button includes opening and closing tags: <button>Delete User</button>.

4fill in blank

hard

Fill both blanks to render a message if user is logged in and show a logout button.

React

function UserPanel({ isLoggedIn }) {
  return (
    <div>
      {isLoggedIn ? [1] : [2]
    </div>
  );
}

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

A<p>Welcome back!</p>

B<button>Logout</button>

C<p>Please log in.</p>

D<button>Login</button>

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the messages for logged in and logged out states.

Using buttons instead of messages in the wrong places.

When logged in, show welcome message; otherwise, ask to log in.

5fill in blank

hard

Fill all three blanks to render a list of items only if the list is not empty, otherwise show 'No items'.

React

function ItemList({ items }) {
  return (
    <div>
      {items.length > 0 ? (
        <ul>
          {items.map([1] => (
            <li key=[2]>[3]</li>
          ))}
        </ul>
      ) : (
        <p>No items</p>
      )}
    </div>
  );
}

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

Aitem

Bitem.id

Citem.name

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using index as key which is not recommended.

Using wrong variable names inside map.

Use item as the map parameter, item.id as the key, and item.name as the displayed text.

Practice

1. Why do we need conditional rendering in React applications?

easy

A. To show or hide parts of the UI based on app state or user actions

B. To make the app load faster by skipping components

C. To style components with CSS dynamically

D. To automatically fix bugs in the code

Solution

1. Step 1: Understand the purpose of conditional rendering

   Conditional rendering lets React show or hide UI parts depending on conditions like user input or app state.

2. Step 2: Compare options with this purpose

   Only To show or hide parts of the UI based on app state or user actions correctly describes this purpose. Other options describe unrelated features.

3. Final Answer:

   To show or hide parts of the UI based on app state or user actions -> Option A

4. Quick Check:

   Conditional rendering = show/hide UI [OK]

Hint: Conditional rendering controls UI visibility based on conditions [OK]

Common Mistakes:

• Confusing conditional rendering with styling
• Thinking it improves app speed directly
• Believing it fixes code errors automatically

2. Which of the following is the correct syntax for conditional rendering using the && operator in React?

easy

A. {condition && <Component />}

B. {condition && &<Component />}

C. {condition ? <Component /> : null}

D. {condition ? <Component />}

Solution

1. Step 1: Review correct syntax for && conditional rendering

   In React, {condition && <Component />} renders the component only if condition is true.

2. Step 2: Check each option for syntax correctness

   {condition && <Component />} matches the correct syntax exactly. {condition && &<Component />} has an extra & symbol. {condition ? <Component /> : null} uses ternary, which is correct but not && syntax. {condition ? <Component />} is incomplete ternary syntax.

3. Final Answer:

   {condition && <Component />} -> Option A

4. Quick Check:

   Correct && syntax = {condition && <Component />} [OK]

Hint: && renders component only if condition is true [OK]

Common Mistakes:

• Adding extra symbols like & accidentally
• Using incomplete ternary syntax
• Confusing ternary and && syntax

3. What will be the output of this React component?

function Greeting({ isLoggedIn }) {
  return (
    <div>
      {isLoggedIn ? <h1>Welcome back!</h1> : <h1>Please sign in.</h1>}
    </div>
  );
}

When isLoggedIn is false?

medium

A. Welcome back!

B. Please sign in.

C. Nothing is rendered

D. Syntax error

Solution

1. Step 1: Understand the ternary condition in the component

   The component uses isLoggedIn ? <h1>Welcome back!</h1> : <h1>Please sign in.</h1>. If isLoggedIn is true, it shows "Welcome back!"; otherwise, it shows "Please sign in."

2. Step 2: Apply the given value false to the condition

   Since isLoggedIn is false, the component renders the second part: <h1>Please sign in.</h1>.

3. Final Answer:

   <h1>Please sign in.</h1> -> Option B

4. Quick Check:

   False condition shows else part [OK]

Hint: Ternary shows first if true, else second [OK]

Common Mistakes:

• Mixing true and false branches
• Thinking nothing renders on false
• Confusing syntax causing errors

4. Identify the error in this React code snippet for conditional rendering:

function ShowMessage({ show }) {
  return (
    <div>
      {show ? <p>Hello!</p>}
    </div>
  );
}

medium

A. No error, code is correct

B. Using && operator incorrectly

C. Missing else part in ternary operator

D. Ternary operator missing colon and else expression

Solution

1. Step 1: Analyze the ternary operator usage

   The code uses {show ? <p>Hello!</p>} which is incomplete because ternary requires both true and false parts separated by a colon.

2. Step 2: Identify correct ternary syntax

   The correct syntax is {show ? <p>Hello!</p> : null} or another expression after colon.

3. Final Answer:

   Ternary operator missing colon and else expression -> Option D

4. Quick Check:

   Ternary needs both parts separated by colon [OK]

Hint: Ternary must have ? and : parts [OK]

Common Mistakes:

• Omitting the else part in ternary
• Confusing ternary with && operator
• Assuming code runs without errors

5. You want to display a special message only if a user is logged in and has admin rights. Which conditional rendering approach is best in React?

hard

A. {isAdmin ? <AdminMessage /> : null}

B. {isLoggedIn ? <AdminMessage /> : <LoginPrompt />}

C. {isLoggedIn && isAdmin && <AdminMessage />}

D. {isLoggedIn || isAdmin ? <AdminMessage /> : null}

Solution

1. Step 1: Understand the condition requirements

   The message should show only if both isLoggedIn and isAdmin are true.

2. Step 2: Evaluate each option's logic

   {isLoggedIn && isAdmin && <AdminMessage />} uses isLoggedIn && isAdmin && <AdminMessage />, which renders the message only if both are true. {isLoggedIn ? <AdminMessage /> : <LoginPrompt />} shows message if logged in regardless of admin. {isAdmin ? <AdminMessage /> : null} ignores logged-in status. {isLoggedIn || isAdmin ? <AdminMessage /> : null} uses OR, showing message if either is true, which is incorrect.

3. Final Answer:

   {isLoggedIn && isAdmin && <AdminMessage />} -> Option C

4. Quick Check:

   Use && to require all conditions true [OK]

Hint: Use && to require all conditions true before rendering [OK]

Common Mistakes:

• Using || instead of && for all conditions
• Ignoring one condition in rendering
• Using ternary without else when needed