Event modifiers (prevent, stop, once) in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to prevent the default form submission behavior.

Vue

<form @submit[1]="submitForm">
  <button type="submit">Send</button>
</form>

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

A.prevent

B.stop

C.once

D.capture

Attempts:

3 left

💡 Hint

Common Mistakes

Using .stop instead of .prevent stops event propagation but not default action.

Using .once does not prevent default behavior.

The .prevent modifier stops the default action, like submitting a form.

2fill in blank

medium

Complete the code to stop the click event from bubbling up.

Vue

<button @click[1]="handleClick">Click me</button>

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

A.stop

B.once

C.prevent

D.self

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prevent only stops default action but not propagation.

Using .once only makes the event fire once, it does not stop bubbling.

The .stop modifier stops the event from bubbling up to parent elements.

3fill in blank

hard

Fix the error in the code to make the click event fire only once.

Vue

<button @click[1]="submit">Submit</button>

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

A.stop

B.prevent

C.once

D.capture

Attempts:

3 left

💡 Hint

Common Mistakes

Using .stop or .prevent does not limit the event to one time.

Forgetting to add any modifier causes the event to fire multiple times.

The .once modifier makes the event listener run only once and then remove itself.

4fill in blank

hard

Fill both blanks to prevent default and stop propagation on a link click.

Vue

<a href="#" @click[1][2]="handleClick">Link</a>

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

A.prevent

B.stop

C.once

D.capture

Attempts:

3 left

💡 Hint

Common Mistakes

Using only one modifier does not fully control the event.

Using .once does not prevent default or stop propagation.

Using .prevent stops the default link navigation, and .stop stops the event from bubbling up.

5fill in blank

hard

Fill all three blanks to create a button that fires once, prevents default, and stops propagation.

Vue

<button @click[1][2][3]="doAction">Action</button>

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

A.once

B.prevent

C.stop

D.capture

Attempts:

3 left

💡 Hint

Common Mistakes

Missing one or more modifiers causes incomplete event control.

Using .capture is unrelated to these behaviors.

The modifiers .once, .prevent, and .stop together make the event fire once, prevent default behavior, and stop bubbling.

Practice

1. What does the .prevent event modifier do in Vue?

easy

A. Delays the event handler execution

B. Stops the default browser action for the event

C. Runs the event handler only once

D. Stops the event from bubbling up the DOM tree

Solution

1. Step 1: Understand the purpose of .prevent

   The .prevent modifier is used to stop the default action the browser takes when an event happens, like submitting a form or following a link.

2. Step 2: Compare with other modifiers

   .stop stops event bubbling, and .once runs the handler once, so they do not match the behavior of .prevent.

3. Final Answer:

   Stops the default browser action for the event -> Option B

4. Quick Check:

   .prevent stops default action [OK]

Hint: Remember: prevent stops default browser actions [OK]

Common Mistakes:

• Confusing .prevent with .stop
• Thinking .prevent runs handler once
• Assuming .prevent delays event

2. Which of the following is the correct syntax to use the .once modifier on a button click event in Vue?

easy

A. Click me

B. Click me

C. Click me

D. Click me

Solution

1. Step 1: Recall Vue event modifier syntax

   Modifiers come after the event name separated by a dot, like @click.once.

2. Step 2: Check each option's syntax

   <button @click.once="handleClick">Click me</button> uses correct syntax. <button @once.click="handleClick">Click me</button> reverses modifier and event. <button v-on:once-click="handleClick">Click me</button> uses invalid directive. <button @click.once()="handleClick">Click me</button> adds parentheses incorrectly.

3. Final Answer:

   <button @click.once="handleClick">Click me</button> -> Option A

4. Quick Check:

   Correct modifier syntax = Click me [OK]

Hint: Event.modifier order is event then dot then modifier [OK]

Common Mistakes:

• Placing modifier before event name
• Adding parentheses after modifier
• Using invalid directive names

3. Consider this Vue template snippet:

<button @click.once.prevent="submitForm">Submit</button>

What will happen when the button is clicked twice quickly?

medium

A. The form submits once, default action prevented once

B. The form submits twice, default action prevented both times

C. The form submits once, default action not prevented

D. The form does not submit at all

Solution

1. Step 1: Analyze the modifiers .once and .prevent

   .once ensures the handler runs only once. .prevent stops the default browser action on that event.

2. Step 2: Understand the combined effect on two clicks

   On first click, submitForm runs and default action is prevented. On second click, handler does not run due to .once, so no submit occurs.

3. Final Answer:

   The form submits once, default action prevented once -> Option A

4. Quick Check:

   .once runs once + .prevent stops default [OK]

Hint: Once runs handler once; prevent stops default each time [OK]

Common Mistakes:

• Thinking .once allows multiple runs
• Assuming .prevent only works once
• Ignoring combined effect of modifiers

4. You have this Vue code:

<div @click.stop="outerClick">
  <button @click="innerClick">Click</button>
</div>

Clicking the button triggers which handlers?

medium

A. Only outerClick runs; innerClick is stopped

B. Both innerClick and outerClick run

C. Only innerClick runs; outerClick is stopped

D. Neither handler runs

Solution

1. Step 1: Understand .stop on the outer div click

   The .stop modifier on the outer div's click event stops the event from bubbling up beyond the div.

2. Step 2: Trace event when button is clicked

   Clicking the button triggers innerClick. The event bubbles to the div, triggering outerClick, but .stop prevents further bubbling beyond the div.

3. Final Answer:

   Only innerClick runs; outerClick is stopped -> Option C

4. Quick Check:

   .stop stops bubbling beyond element [OK]

Hint: Stop stops bubbling beyond element with modifier [OK]

Common Mistakes:

• Thinking .stop stops inner handler
• Thinking .stop prevents the outer handler from running
• Confusing event bubbling direction

5. You want a button that submits a form only once, prevents default submission, and stops the click event from bubbling. Which Vue event modifiers should you use?

hard

A. @click.prevent.once

B. @click.stop.once

C. @click.stop.prevent

D. @click.once.prevent.stop

Solution

1. Step 1: Identify required modifiers and order

   You need .once to run handler once, .prevent to stop default form submission, and .stop to stop event bubbling. The correct order is event name then modifiers separated by dots.

2. Step 2: Check each option's correctness

   @click.once.prevent.stop uses correct syntax and includes all required modifiers. Other options miss one of the modifiers.

3. Final Answer:

   @click.once.prevent.stop -> Option D

4. Quick Check:

   Correct modifier order: event.once.prevent.stop [OK]

Hint: Use event.once.prevent.stop in that order [OK]

Common Mistakes:

• Changing modifier order incorrectly
• Using invalid modifier syntax
• Forgetting one of the needed modifiers