Transition directive (transition:fade) in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the transition:fade directive do in Svelte?

It smoothly changes the opacity of an element when it enters or leaves the DOM, creating a fading effect.

beginner

How do you apply a fade transition to an element in Svelte?

Add transition:fade inside the element's tag, like <div transition:fade>...</div>.

intermediate

Can you customize the duration of the fade transition in Svelte? How?

Yes, by passing an object with options like { duration: 500 } to fade, e.g., transition:fade={{ duration: 500 }}.

beginner

What happens if you remove an element with transition:fade applied?

The element fades out smoothly before it is removed from the DOM.

beginner

Why is using transition:fade better than instantly hiding elements?

Because it creates a smooth visual effect that is easier on the eyes and improves user experience by showing changes clearly.

What does transition:fade control in Svelte?

A Opacity of an element during enter and leave

B Position of an element on the screen

C Background color change

D Font size animation

transition:fade changes the opacity smoothly when elements appear or disappear.

How do you specify a 1-second fade duration in Svelte?

A <code>transition:fade(1000)</code>

B <code>transition:fade={{ duration: 1000 }}</code>

C <code>fade-duration=1000</code>

D <code>transition:fade-duration=1000</code>

You pass an object with duration in milliseconds inside double curly braces.

When does the fade-out effect happen?

A When the element is added to the DOM

B When the page loads

C When the element is clicked

D When the element is removed from the DOM

The fade-out happens as the element leaves the DOM, making it disappear smoothly.

Which import is needed to use fade in Svelte?

A <code>import { fade } from 'svelte/effects';</code>

B <code>import fade from 'svelte/fade';</code>

C <code>import { fade } from 'svelte/transition';</code>

D No import needed

You must import fade from svelte/transition to use it.

What is the default duration of fade transition if not specified?

A 400 milliseconds

B 1000 milliseconds

C 200 milliseconds

D No duration, instant

The default fade duration in Svelte is 400ms if you don't set it.

Explain how to add a fade transition to an element in Svelte and customize its duration.

Think about the directive syntax and import statement.

Describe what happens visually when an element with transition:fade is removed from the page.

Focus on the fade-out behavior.

Practice

1. What does the transition:fade directive do in Svelte?

easy

A. It instantly hides elements without animation.

B. It moves elements from left to right.

C. It changes the color of elements gradually.

D. It makes elements smoothly appear and disappear by fading.

Solution

1. Step 1: Understand the purpose of transition:fade

   This directive is used to animate elements so they fade in or out smoothly when they appear or disappear.

2. Step 2: Compare with other options

   The options describing movement from left to right and changing color gradually describe different animations, and the option describing instant hiding describes no animation. Only the fading description is correct.

3. Final Answer:

   It makes elements smoothly appear and disappear by fading. -> Option D

4. Quick Check:

   transition:fade = smooth fade in/out [OK]

Hint: Fade means smooth appear/disappear by changing opacity [OK]

Common Mistakes:

• Confusing fade with movement or color change
• Thinking fade hides elements instantly
• Assuming fade only works on text

2. Which of the following is the correct syntax to apply a fade transition with a duration of 500ms to a <div> in Svelte?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall correct object syntax in Svelte transitions

   The options object uses JavaScript object notation with colon and number value, no quotes or units.

2. Step 2: Check each option's syntax

   <div transition:fade={{ duration: 500 }}></div> uses correct syntax: { duration: 500 }. The option with {{duration=500}} uses = instead of :, the option with duration: '500' uses quotes around the number, and the option with duration: 500ms adds invalid 'ms' unit.

3. Final Answer:

   <div transition:fade={{ duration: 500 }}></div> -> Option A

4. Quick Check:

   Use colon and number for options object [OK]

Hint: Use colon and number for options, no quotes or units [OK]

Common Mistakes:

• Using = instead of : in object
• Putting quotes around numeric values
• Adding units like 'ms' inside options

3. Consider this Svelte code snippet:

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

<button on:click={() => visible = !visible}>Toggle</button>

{#if visible}
  <div transition:fade>Hello</div>
{/if}

What happens when you click the button?

medium

A. The <div> instantly appears and disappears without animation.

B. Nothing changes because the transition is missing duration.

C. The <div> fades in and out smoothly each time the button is clicked.

D. The <div> slides in from the left when shown.

Solution

1. Step 1: Understand the toggle and transition

   Clicking the button toggles the visible variable, which controls if the <div> is shown or hidden. The transition:fade applies a fade animation on enter and leave.

2. Step 2: Analyze the effect of transition:fade without duration

   By default, fade uses a standard duration, so the <div> fades smoothly in and out on toggle.

3. Final Answer:

   The <div> fades in and out smoothly each time the button is clicked. -> Option C

4. Quick Check:

   transition:fade animates fade in/out on toggle [OK]

Hint: Toggle with fade makes smooth appear/disappear [OK]

Common Mistakes:

• Thinking fade requires explicit duration
• Expecting slide animation instead of fade
• Assuming no animation happens on toggle

4. This Svelte code tries to fade a paragraph but does not work:

<p transition:fade duration=300>Hello</p>

What is the error and how to fix it?

medium

A. Missing curly braces around options object; fix: transition:fade={{ duration: 300 }}

B. Duration value must be a string; fix: duration='300'

C. transition:fade cannot be used on <p> elements; use <div> instead

D. The fade transition requires importing from 'svelte/animate' instead of 'svelte/transition'

Solution

1. Step 1: Identify the syntax error in transition options

   The code uses transition:fade duration=300 which is invalid syntax. Options must be passed as an object inside curly braces.

2. Step 2: Correct syntax for passing options

   The correct way is transition:fade={{ duration: 300 }} with double curly braces and colon.

3. Final Answer:

   Missing curly braces around options object; fix: transition:fade={{ duration: 300 }} -> Option A

4. Quick Check:

   Options need curly braces and colon syntax [OK]

Hint: Options must be inside {{ }} with colon, not bare attributes [OK]

Common Mistakes:

• Passing options without curly braces
• Using = instead of : inside options
• Wrong import source for fade transition

5. You want a list of items to fade in one by one with a 200ms delay between each fade using transition:fade. Which approach correctly applies this in Svelte?

hard

A. Use {#each items as item}<li transition:fade={{ delay: 200 }}>{item}</li>{/each} without index

B. Use {#each items as item, i}<li transition:fade={{ delay: i * 200 }}>{item}</li>{/each}

C. Use {#each items as item}<li transition:fade={{ duration: i * 200 }}>{item}</li>{/each} with duration instead of delay

D. Use {#each items as item}<li transition:fade={{ delay: 200 * items.length }}>{item}</li>{/each} same delay for all

Solution

1. Step 1: Understand how to stagger fade transitions

   To fade items one by one, each item needs a delay increasing by 200ms times its index.

2. Step 2: Check each option's delay usage

   Use {#each items as item, i}<li transition:fade={{ delay: i * 200 }}>{item}</li>{/each} uses the index i to multiply delay, correctly staggering fades. Use {#each items as item}<li transition:fade={{ delay: 200 }}>{item}</li>{/each} without index uses fixed delay, so all fade together. Use {#each items as item}<li transition:fade={{ duration: i * 200 }}>{item}</li>{/each} with duration instead of delay incorrectly uses duration for delay. Use {#each items as item}<li transition:fade={{ delay: 200 * items.length }}>{item}</li>{/each} same delay for all applies same delay to all.

3. Final Answer:

   Use {#each items as item, i}<li transition:fade={{ delay: i * 200 }}>{item}</li>{/each} -> Option B

4. Quick Check:

   Use index-based delay for staggered fade [OK]

Hint: Multiply delay by index to stagger fades [OK]

Common Mistakes:

• Using fixed delay for all items
• Confusing duration with delay
• Not using index in each block