Ternary operator usage in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to render 'Yes' if isActive is true, otherwise 'No'.

React

return <div>{isActive ? [1] : 'No'}</div>;

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

A'Yes'

B'No'

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Putting 'No' in both places so it never shows 'Yes'.

Using boolean true instead of string 'Yes'.

The ternary operator checks if isActive is true. If yes, it renders 'Yes', else 'No'.

2fill in blank

medium

Complete the code to display 'Logged in' if user exists, otherwise 'Guest'.

React

return <p>{user ? [1] : 'Guest'}</p>;

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

A'Logged in'

B'Guest'

Cuser.name

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the true and false parts.

Using user.name without checking if user exists.

The ternary operator shows 'Logged in' when user is truthy, else 'Guest'.

3fill in blank

hard

Fix the error in the ternary expression to render 'Active' if status equals 'active', else 'Inactive'.

React

return <span>{status === 'active' [1] 'Active' : 'Inactive'}</span>;

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

A==

B&&

C?

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using '&&' instead of '?'.

Using '==' instead of '?'.

The ternary operator requires a question mark '?' after the condition before the true value.

4fill in blank

hard

Fill both blanks to render 'Welcome, Admin' if role is 'admin', else 'Welcome, User'.

React

return <h1>{role [1] 'admin' [2] 'Welcome, Admin' : 'Welcome, User'}</h1>;

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

A===

B!==

C?

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '===' for comparison.

Using '&&' instead of '?'.

Use '===' to compare role to 'admin', then '?' for the ternary operator.

5fill in blank

hard

Fill all three blanks to render the user's name if user exists, else 'Guest', and add a period at the end.

React

return <p>{user [1] 'name' [2] user.name [3] '.' : 'Guest'}</p>;

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

A?

B:

C+

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Using '?' instead of '&&' for existence check.

Forgetting to concatenate the period.

Use '&&' to check if user exists, then '?' and ':' for ternary, and '+' to concatenate the period.

Practice

1. What does the ternary operator condition ? expr1 : expr2 do in React JSX?

easy

A. It chooses expr1 if condition is true, otherwise expr2.

B. It always returns expr2 regardless of the condition.

C. It runs both expr1 and expr2 and returns an array.

D. It throws an error if condition is false.

Solution

1. Step 1: Understand ternary operator structure

   The ternary operator has the form condition ? expr1 : expr2, which means it evaluates the condition first.

2. Step 2: Evaluate the condition result

   If the condition is true, it returns expr1; if false, it returns expr2.

3. Final Answer:

   It chooses expr1 if condition is true, otherwise expr2. -> Option A

4. Quick Check:

   Ternary operator = choose between two values [OK]

Hint: Remember: condition ? trueValue : falseValue [OK]

Common Mistakes:

• Thinking it runs both expressions
• Confusing with logical AND/OR operators
• Using it outside JSX incorrectly

2. Which of the following is the correct syntax to use a ternary operator inside JSX to display "Yes" if isActive is true, else "No"?

easy

A. {isActive ? "Yes"; "No"}

B. {isActive ? "Yes" : "No"}

C. {isActive ? "Yes"}

D. {isActive : "Yes" ? "No"}

Solution

1. Step 1: Check ternary operator syntax in JSX

   The ternary operator must be inside curly braces in JSX and follow condition ? expr1 : expr2 format.

2. Step 2: Validate each option

   {isActive ? "Yes" : "No"} correctly uses {isActive ? "Yes" : "No"}. Options B, C, and D have syntax errors or incomplete expressions.

3. Final Answer:

   {isActive ? "Yes" : "No"} -> Option B

4. Quick Check:

   Correct JSX ternary syntax = {isActive ? "Yes" : "No"} [OK]

Hint: Use curly braces and ? : inside JSX [OK]

Common Mistakes:

• Missing colon ':' in ternary
• Using semicolon instead of colon
• Not wrapping expression in curly braces

3. What will this React component render?

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

If isLoggedIn is false?

medium

A. Please sign in.

B. Welcome back!

C.

D. SyntaxError

Solution

1. Step 1: Understand the ternary condition

   The component uses isLoggedIn ? <h1>Welcome back!</h1> : <h1>Please sign in.</h1>. If isLoggedIn is false, it chooses the second expression.

2. Step 2: Determine output when isLoggedIn is false

   Since isLoggedIn is false, it renders <h1>Please sign in.</h1> inside the div.

3. Final Answer:

   <div><h1>Please sign in.</h1></div> -> Option A

4. Quick Check:

   False condition shows second expression [OK]

Hint: False condition picks expression after colon ':' [OK]

Common Mistakes:

• Choosing first expression for false condition
• Confusing JSX tags rendering
• Expecting empty div output

4. Identify the error in this JSX snippet:

return (
  <div>
    {isReady ? <p>Ready</p> : <p>Not ready</p>}
    {isReady ? <p>Go!</p> : null}
  </div>
);

medium

A. Ternary operator cannot be used inside JSX.

B. JSX elements must not be inside curly braces.

C. Second ternary is missing the else part after colon.

D. No error; code is valid.

Solution

1. Step 1: Check each ternary usage

   The first ternary is correct with both true and false parts. The second uses {isReady ? <p>Go!</p> : null} which is valid syntax.

2. Step 2: Understand ternary operator requirements

   The ternary operator requires both true and false expressions separated by a colon. Here, the else part is null, which is valid JSX.

3. Final Answer:

   No error; code is valid. -> Option D

4. Quick Check:

   Ternary needs both ? and : parts, and else can be null [OK]

Hint: Ternary always needs ? and : parts [OK]

Common Mistakes:

• Omitting the else expression
• Confusing ternary with logical AND
• Thinking JSX can't have ternary

5. You want to display a list of user names with a label showing if they are online or offline using ternary inside JSX. Which code correctly implements this?

const users = [
  { name: "Alice", online: true },
  { name: "Bob", online: false }
];

function UserList() {
  return (
    <ul>
      {users.map(user => (
        <li key={user.name}>
          {user.name} - {user.online ? "Online" : "Offline"}
        </li>
      ))}
    </ul>
  );
}

hard

A. Does not render anything because key is missing.

B. Will throw an error because ternary cannot be used inside map.

C. Correctly shows each user with "Online" or "Offline" label.

D. Only shows "Online" for all users regardless of status.

Solution

1. Step 1: Analyze the map and ternary usage

   The code maps over users and uses a ternary to show "Online" if user.online is true, else "Offline".

2. Step 2: Check React key and JSX correctness

   Each <li> has a unique key from user.name, and the ternary is correctly inside JSX curly braces.

3. Final Answer:

   Correctly shows each user with "Online" or "Offline" label. -> Option C

4. Quick Check:

   Map + ternary inside JSX = correct rendering [OK]

Hint: Use map with ternary inside JSX for conditional labels [OK]

Common Mistakes:

• Forgetting unique key in list items
• Trying to use ternary outside JSX braces
• Assuming ternary can't be used in map