Deferred transitions in Svelte - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a deferred transition is used in Svelte?

Consider a Svelte component using transition:fade with defer. What is the visible effect when the component is removed?

Svelte

<script>
  import { fade } from 'svelte/transition';
  let visible = true;
</script>
<button on:click={() => visible = !visible}>Toggle</button>
{#if visible}
  <div transition:fade={{ duration: 400, defer: true }}>
    Hello with deferred fade
  </div>
{/if}

A The element does not fade out at all and disappears instantly.

B The element waits for the next animation frame before starting to fade out.

C The element fades out immediately when removed.

D The element fades in but never fades out.

💡 Hint

Deferred transitions delay the start of the animation slightly.

Using defer: true delays the start of the transition until the next animation frame, making the fade out start slightly later than usual.

📝 Syntax

intermediate

Which syntax correctly applies a deferred transition in Svelte?

Choose the correct way to apply a deferred slide transition with duration 300ms.

A <div transition:slide={{ duration: 300 defer: true }}>Content</div>

B <div transition:slide={{ defer: true, duration: 300 }}>Content</div>

C <div transition:slide={{ duration: 300, defer: true }}>Content</div>

D <div transition:slide={{ duration: 300; defer: true }}>Content</div>

💡 Hint

Options inside an object must be separated by commas.

The correct syntax uses a JavaScript object with comma-separated key-value pairs inside double curly braces.

🔧 Debug

advanced

Why does this deferred transition not start on removal?

Given this code, why does the fade transition not run when the element is removed?

Svelte

<script>
  import { fade } from 'svelte/transition';
  let show = true;
</script>
<button on:click={() => show = false}>Hide</button>
{#if show}
  <p transition:fade={{ defer: true, duration: 500 }}>Goodbye!</p>
{/if}

A The element is removed before the deferred transition can start.

B The defer option disables the fade out transition completely.

C The fade transition requires an explicit key to work with defer.

D The duration must be set to 0 for deferred transitions to run.

💡 Hint

Think about when the element is removed from the DOM versus when the transition starts.

With defer: true, the transition waits for the next animation frame. If the element is removed immediately, the transition never starts.

❓ state_output

advanced

What is the state of the element during a deferred transition?

When using defer: true on a transition, what is the element's state during the delay before the transition starts?

A The element is fully visible and unchanged until the transition starts.

B The element is hidden immediately and then fades in after the delay.

C The element is partially transparent during the delay period.

D The element is removed from the DOM during the delay.

💡 Hint

Deferred means the transition is delayed, not that the element changes immediately.

During the deferred delay, the element remains fully visible and unchanged until the transition actually begins.

🧠 Conceptual

expert

Why use deferred transitions in Svelte?

Which reason best explains why a developer would choose to use defer: true in a Svelte transition?

A To make the transition run instantly without any delay or animation effect.

B To force the transition to run twice for a stronger visual effect.

C To disable the transition on initial render but enable it on removal only.

D To delay the start of the transition to avoid layout thrashing and improve animation smoothness.

💡 Hint

Think about performance and animation timing.

Deferred transitions delay the start to the next animation frame, helping prevent layout thrashing and making animations smoother.