Flip animations in Svelte - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when the FLIP animation is applied to a list reorder?

Consider a Svelte component that uses the flip animation on a list of items. What is the visible effect when the list order changes?

Svelte

<script>
  import { flip } from 'svelte/animate';
  let items = ['A', 'B', 'C'];
  function reorder() {
    items = ['C', 'A', 'B'];
  }
</script>

<ul>
  {#each items as item (item)}
    <li animate:flip>{item}</li>
  {/each}
</ul>
<button on:click={reorder}>Reorder</button>

A The items instantly jump to their new positions without any animation.

B The items smoothly move from their old positions to new positions with a sliding effect.

C The items fade out and fade back in without moving positions.

D The items rotate 360 degrees in place without changing position.

💡 Hint

Think about what the FLIP technique is designed to do: it animates position changes smoothly.

The FLIP animation in Svelte animates elements moving from their old position to their new position smoothly, creating a sliding effect when list items reorder.

📝 Syntax

intermediate

Which option correctly applies the FLIP animation to a Svelte list?

Choose the correct syntax to apply the FLIP animation to each item in a Svelte list.

Svelte

<script>
  import { flip } from 'svelte/animate';
  let items = [1, 2, 3];
</script>

<ul>
  {#each items as item (item)}
    <!-- Which line correctly applies flip animation? -->
    <li>...</li>
  {/each}
</ul>

A <li animate:flip>{item}</li>

B <li use:flip>{item}</li>

C <li transition:flip>{item}</li>

D <li in:flip>{item}</li>

💡 Hint

Remember that FLIP is an animation, not a transition or action.

In Svelte, the FLIP animation is applied using animate:flip directive on elements that change position.

🔧 Debug

advanced

Why does the FLIP animation not run when list items lack keys?

Given this Svelte list with FLIP animation, why does the animation not trigger when reordering?

Svelte

<script>
  import { flip } from 'svelte/animate';
  let items = ['x', 'y', 'z'];
  function shuffle() {
    items = ['z', 'x', 'y'];
  }
</script>

<ul>
  {#each items as item}
    <li animate:flip>{item}</li>
  {/each}
</ul>
<button on:click={shuffle}>Shuffle</button>

A Because the shuffle function does not update the items array correctly.

B Because the flip animation requires a transition directive instead of animate.

C Because the list items lack unique keys, Svelte cannot track their positions for FLIP animation.

D Because FLIP animation only works on elements with CSS position set to absolute.

💡 Hint

Think about how Svelte tracks elements in a list for animations.

Svelte needs unique keys in the {#each} block to track elements and animate their position changes with FLIP. Without keys, it cannot detect moves.

❓ state_output

advanced

What is the final order of items after this FLIP animation sequence?

Given this Svelte component, what is the order of items displayed after clicking the button twice?

Svelte

<script>
  import { flip } from 'svelte/animate';
  let items = ['1', '2', '3'];
  function rotate() {
    items = [...items.slice(1), items[0]];
  }
</script>

<ul>
  {#each items as item (item)}
    <li animate:flip>{item}</li>
  {/each}
</ul>
<button on:click={rotate}>Rotate</button>

A ['3', '1', '2']

B ['1', '2', '3']

C ['2', '3', '1']

D ['3', '2', '1']

💡 Hint

Each click moves the first item to the end. Think step by step.

First click: ['2', '3', '1']
Second click: ['3', '1', '2']

🧠 Conceptual

expert

Why is the FLIP animation technique efficient for animating layout changes?

Choose the best explanation for why FLIP animations are efficient when animating elements that change position.

A FLIP disables CSS transitions and uses JavaScript timers to animate positions.

B FLIP uses opacity changes to hide and show elements, which is faster than moving them.

C FLIP forces the browser to repaint the entire page to ensure smooth animation.

D FLIP calculates the difference between first and last positions and animates only the transform, avoiding layout thrashing.

💡 Hint

Think about how browsers handle layout and paint during animations.

FLIP stands for First, Last, Invert, Play. It animates elements by calculating position differences and applying transforms, which is GPU-accelerated and avoids costly layout recalculations.