JavaScript hooks for transitions in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a JavaScript hook for the enter transition in Vue.

Vue

<template>
  <transition @before-enter="[1]">
    <div v-if="show">Hello</div>
  </transition>
</template>

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

AstartEnter

BenterHook

ConEnter

DbeforeEnterHook

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect hook names like 'enterHook' which don't match the event.

Forgetting to bind the hook method in the component.

The @before-enter event expects a method name like beforeEnterHook to run before the enter transition starts.

2fill in blank

medium

Complete the code to define the JavaScript hook method for the leave transition.

Vue

<script setup>
import { ref } from 'vue'
const show = ref(true)

function [1](el, done) {
  el.style.opacity = 0
  setTimeout(() => {
    done()
  }, 300)
}
</script>

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

Aleave

BleaveHook

CbeforeLeave

DonLeave

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'leaveHook' which is not a recognized Vue hook name.

Not calling the done callback to finish the transition.

The leave hook is called when the leave transition starts. It receives the element and a done callback.

3fill in blank

hard

Fix the error in the transition hook usage by completing the code.

Vue

<template>
  <transition @[1]="fadeOut">
    <p v-if="visible">Goodbye</p>
  </transition>
</template>

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

Aleave

Bleave-start

Cbefore-leave

Dafter-leave

Attempts:

3 left

💡 Hint

Common Mistakes

Using dash-separated event names like 'leave-start' which are invalid.

Confusing lifecycle hooks with transition events.

The correct event for the leave transition hook is @leave. Other options are invalid event names.

4fill in blank

hard

Fill both blanks to correctly use JavaScript hooks for enter and leave transitions.

Vue

<template>
  <transition @[1]="onEnter" @[2]="onLeave">
    <div v-if="active">Content</div>
  </transition>
</template>

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

Aenter

Bleave

CbeforeEnter

DafterLeave

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing lifecycle hooks with transition event names.

Using 'beforeEnter' or 'afterLeave' which are not event names.

The @enter and @leave events trigger the JavaScript hooks for entering and leaving transitions.

5fill in blank

hard

Fill all three blanks to create a transition with JavaScript hooks for before-enter, enter, and after-leave.

Vue

<template>
  <transition
    @[1]="beforeEnter"
    @[2]="enter"
    @[3]="afterLeave"
  >
    <span v-if="show">Hi!</span>
  </transition>
</template>

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

Abefore-enter

Benter

Cafter-leave

Dleave

Attempts:

3 left

💡 Hint

Common Mistakes

Using camelCase event names in the template which won't work.

Confusing 'leave' with 'after-leave' event names.

Vue transition events use kebab-case names like before-enter, enter, and after-leave for JavaScript hooks.

Practice

1. What is the main purpose of JavaScript hooks in Vue transitions?

easy

A. To run custom code at specific moments during enter and leave transitions

B. To replace CSS animations completely

C. To define the HTML structure of a component

D. To manage Vue component state

Solution

1. Step 1: Understand what JavaScript hooks do in Vue transitions

   JavaScript hooks allow you to run code at key moments during the enter and leave phases of a transition.

2. Step 2: Compare options with this understanding

   Only To run custom code at specific moments during enter and leave transitions correctly describes this purpose. Options B, C, and D describe unrelated concepts.

3. Final Answer:

   To run custom code at specific moments during enter and leave transitions -> Option A

4. Quick Check:

   JavaScript hooks = run code during transitions [OK]

Hint: Hooks run code during enter/leave, not replace CSS [OK]

Common Mistakes:

• Thinking hooks replace CSS animations
• Confusing hooks with component state management
• Believing hooks define HTML structure

2. Which of the following is the correct syntax to define a JavaScript hook for the beforeEnter phase in a Vue transition component?

easy

A. <transition v-on:before-enter="myHook">

B. <transition v-on:beforeEnter="myHook">

C. <transition @before-enter="myHook">

D. <transition @beforeEnter="myHook">

Solution

1. Step 1: Recall Vue event naming conventions for transitions

   Vue uses kebab-case event names for transition hooks, like before-enter, and the shorthand @ for v-on:.

2. Step 2: Match the correct syntax

   <transition @before-enter="myHook"> uses @before-enter, which is correct. Options A, C, and D use camelCase or incorrect casing.

3. Final Answer:

   <transition @before-enter="myHook"> -> Option C

4. Quick Check:

   Vue transition hooks use kebab-case with @ [OK]

Hint: Use kebab-case and @ for Vue transition hooks [OK]

Common Mistakes:

• Using camelCase event names
• Mixing v-on: and @ incorrectly
• Capitalizing event names

3. Given this Vue transition component snippet, what will be logged when the element starts entering?

<transition @enter="onEnter">
  <div v-if="show">Hello</div>
</transition>

medium

A. Nothing is logged because show is initially false

B. Throws an error because done() is called synchronously

C. Logs 'Enter started' immediately on page load

D. Logs 'Enter started' after 1 second when element appears

Solution

1. Step 1: Understand the timing of the show variable

   Initially, show is false, so the element is not rendered. After 1 second, show becomes true, triggering the enter transition.

2. Step 2: Analyze the enter hook behavior

   The onEnter hook logs 'Enter started' and calls done() immediately. This happens after 1 second when the element appears.

3. Final Answer:

   Logs 'Enter started' after 1 second when element appears -> Option D

4. Quick Check:

   Enter hook logs on element show [OK]

Hint: Enter hook runs when element appears, not on load [OK]

Common Mistakes:

• Thinking enter hook runs immediately on load
• Assuming no log because initial show is false
• Believing done() call causes error

4. Identify the error in this Vue transition JavaScript hook code:

<transition @leave="onLeave">
  <div v-if="visible">Bye</div>
</transition>

medium

A. Calling done() immediately before animation finishes causes transition to end too soon

B. Missing a return statement in onLeave function

C. Using setTimeout inside onLeave is not allowed

D. v-if should be v-show for transitions

Solution

1. Step 1: Understand the leave hook timing

   The onLeave hook should call done() only after the animation finishes to keep the element during transition.

2. Step 2: Analyze the code's done() call

   Here, done() is called immediately, but the opacity change happens after 500ms, so the transition ends too soon.

3. Final Answer:

   Calling done() immediately before animation finishes causes transition to end too soon -> Option A

4. Quick Check:

   done() must wait for animation end [OK]

Hint: Call done() only after animation completes [OK]

Common Mistakes:

• Calling done() too early
• Confusing v-if and v-show for transitions
• Thinking setTimeout is disallowed in hooks

5. You want to create a fade transition that delays the leave animation until a custom API call finishes. Which approach correctly uses JavaScript hooks to achieve this?

<transition @leave="handleLeave">
  <div v-if="show">Content</div>
</transition>

<script setup>
const show = ref(true)
async function apiCall() {
  return new Promise(resolve => setTimeout(resolve, 1000))
}

function handleLeave(el, done) {
  // What should go here?
}
</script>

hard

A. Set opacity to 0, call done(), then call apiCall()

B. Call apiCall(), then in .then() set opacity to 0 and call done()

C. Call done() immediately, then call apiCall()

D. Do nothing in handleLeave; rely on CSS only

Solution

1. Step 1: Understand the goal

   The leave transition should wait for the API call to finish before starting the fade out and completing the transition.

2. Step 2: Use async logic in the leave hook

   Call apiCall(), then after it resolves, set opacity to 0 and call done() to signal transition end.

3. Final Answer:

   Call apiCall(), then in .then() set opacity to 0 and call done() -> Option B

4. Quick Check:

   Wait async, then animate and done() [OK]

Hint: Wait async call before done() in leave hook [OK]

Common Mistakes:

• Calling done() before async finishes
• Ignoring async and relying on CSS only
• Calling done() too early, skipping animation