Conditional classes (class:name) in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add the class 'active' only when the variable isActive is true.

Svelte

<button class:[1]={isActive}>Click me</button>

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

Aselected

Bactive

Cenabled

Dhighlight

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong class name after class:.

Forgetting to use curly braces around the condition.

The syntax class:active={isActive} adds the 'active' class only when isActive is true.

2fill in blank

medium

Complete the code to add the class 'hidden' only when the variable isHidden is true.

Svelte

<div class:[1]={isHidden}>Content</div>

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

Ashow

Bvisible

Chidden

Ddisplay

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name that does not exist in CSS.

Not wrapping the condition in curly braces.

Using class:hidden={isHidden} will add the 'hidden' class only when isHidden is true.

3fill in blank

hard

Fix the error in the code to correctly add the class 'error' when hasError is true.

Svelte

<p class:[1]={hasError}>Warning message</p>

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

Aerror

Bwarning

Calert

Dfail

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different class name than 'error'.

Not using the correct variable for the condition.

The class name after class: must be 'error' to match the intended CSS class.

4fill in blank

hard

Fill both blanks to add 'active' class when isActive is true and 'disabled' class when isDisabled is true.

Svelte

<button class:[1]={isActive} class:[2]={isDisabled}>Submit</button>

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

Aactive

Benabled

Cdisabled

Dselected

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping class names between variables.

Using class names that do not exist in CSS.

Use class:active={isActive} and class:disabled={isDisabled} to toggle classes based on variables.

5fill in blank

hard

Fill all three blanks to add 'highlight' when isHighlighted is true, 'selected' when isSelected is true, and 'focus' when isFocused is true.

Svelte

<div class:[1]={isHighlighted} class:[2]={isSelected} class:[3]={isFocused}>Item</div>

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

Ahighlight

Bselected

Cfocus

Dactive

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up class names and variables.

Forgetting to use curly braces for conditions.

Each class name matches the variable controlling its presence: highlight, selected, and focus.

Practice

1. What does the Svelte syntax class:active={isActive} do in a component?

easy

A. Always adds the CSS class 'active' regardless of isActive value.

B. Adds the CSS class 'active' only if the variable isActive is true.

C. Removes the CSS class 'active' when isActive is true.

D. Adds the CSS class 'active' only if isActive is false.

Solution

1. Step 1: Understand the syntax class:name={condition}

   This syntax adds the CSS class name only when the condition is true.

2. Step 2: Apply to class:active={isActive}

   The class active is added only if isActive is true; otherwise, it is not added.

3. Final Answer:

   Adds the CSS class 'active' only if the variable isActive is true. -> Option B

4. Quick Check:

   Conditional class = Adds class if true [OK]

Hint: class:name adds class only when condition is true [OK]

Common Mistakes:

• Thinking class:name adds class always
• Confusing true and false conditions
• Assuming it removes class when true

2. Which of the following is the correct syntax to conditionally add a CSS class highlight in Svelte when isHighlighted is true?

easy

A. class:highlight = {isHighlighted}

B. class.highlight={isHighlighted}

C. class:highlight={isHighlighted}

D. class={highlight: isHighlighted}

Solution

1. Step 1: Recall correct Svelte conditional class syntax

   The correct syntax is class:name={condition} without spaces around the equals sign.

2. Step 2: Check each option

   class:highlight={isHighlighted} matches the correct syntax exactly: class:highlight={isHighlighted}. Others have syntax errors or invalid formats.

3. Final Answer:

   class:highlight={isHighlighted} -> Option C

4. Quick Check:

   Correct syntax = class:name={condition} [OK]

Hint: No spaces around = in class:name={condition} [OK]

Common Mistakes:

• Adding spaces around = sign
• Using dot instead of colon
• Trying object syntax inside class attribute

3. Given this Svelte code snippet:

<script>
  let isError = false;
</script>

<div class:error={isError} class:success={!isError}>Status</div>

What CSS classes will the <div> have when isError is false?

medium

A. No classes added

B. Only the class error

C. Both classes error and success

D. Only the class success

Solution

1. Step 1: Evaluate class:error={isError} when isError is false

   Since isError is false, the class error is not added.

2. Step 2: Evaluate class:success={!isError} when isError is false

   The expression !isError is true, so the class success is added.

3. Final Answer:

   Only the class success -> Option D

4. Quick Check:

   Negation adds success class when isError is false [OK]

Hint: Check condition true to add class, false to skip [OK]

Common Mistakes:

• Adding both classes regardless of condition
• Confusing negation operator !
• Assuming false adds class

4. Identify the error in this Svelte code:

<script>
  let isActive = true;
</script>

<button class:active = {isActive}>Click Me</button>

medium

A. There should be no spaces around the equals sign in class:active = {isActive}.

B. The class: directive cannot be used on a <button> element.

C. The class name cannot be active.

D. The variable isActive is not declared.

Solution

1. Step 1: Check variable declaration

   The variable isActive is declared correctly in the script block.

2. Step 2: Check syntax of conditional class

   The syntax class:active = {isActive} has spaces around the equals sign, which is invalid in Svelte. It should be class:active={isActive} without spaces.

3. Final Answer:

   There should be no spaces around the equals sign in class:active = {isActive}. -> Option A

4. Quick Check:

   No spaces around = in class:name={condition} [OK]

Hint: No spaces around = in class:name={condition} [OK]

Common Mistakes:

• Adding spaces around = sign
• Thinking class:name can't be on button
• Missing variable declaration

5. You want to add two conditional classes visible and highlight to a <div> in Svelte. visible should be added when isVisible is true, and highlight only when isHighlighted is also true and isVisible is true.

Which of the following is the correct way to write this?

hard

A. <div class:visible={isVisible} class:highlight={isHighlighted && isVisible}>Content</div>

B. <div class:visible={isVisible} class:highlight={isHighlighted || isVisible}>Content</div>

C. <div class:visible={isVisible && isHighlighted} class:highlight={isVisible}>Content</div>

D. <div class:visible={isVisible} class:highlight={isHighlighted}>Content</div>

Solution

1. Step 1: Understand conditions for each class

   The class visible depends only on isVisible. The class highlight depends on both isHighlighted and isVisible being true.

2. Step 2: Check each option's logic

   <div class:visible={isVisible} class:highlight={isHighlighted && isVisible}>Content</div>

   correctly uses class:visible={isVisible} and class:highlight={isHighlighted && isVisible}, matching the requirements.

   <div class:visible={isVisible} class:highlight={isHighlighted || isVisible}>Content</div>

   uses OR which is incorrect.

   <div class:visible={isVisible && isHighlighted} class:highlight={isVisible}>Content</div>

   swaps conditions incorrectly.

   <div class:visible={isVisible} class:highlight={isHighlighted}>Content</div>

   misses the isVisible condition for highlight.

3. Final Answer:

   <div class:visible={isVisible} class:highlight={isHighlighted && isVisible}>Content</div> -> Option A

4. Quick Check:

   Use && to combine conditions for conditional classes [OK]

Hint: Use && to combine multiple conditions in class:name [OK]

Common Mistakes:

• Using || instead of && for combined conditions
• Swapping conditions between classes
• Omitting one condition in combined class