Custom Animations
All Svelte topics∙ Svelte
Custom Animations explains custom transition or animation functions returning CSS or tick behavior for this custom, animations lesson. You will learn its exact Svelte rule, failure mode, verification plan, and production evidence.
Syntax
<div transition:fade>Visible</div>Example
// Topic: Custom Animations
const transition = { name: 'fade', duration: 200 };
console.log(transition.name + ':' + transition.duration);
// Expected Output: fade:200Expected Output
fade:200Line-by-line
| Line | Meaning |
|---|---|
const transition = { name: 'fade', duration: 200 }; | Defines state, behavior, or output for this Svelte example. |
console.log(transition.name + ':' + transition.duration); | Prints the expected result for this Svelte lesson. |
Real-World Uses
- 1Custom Animations is used for menus, notifications, reordered lists, and drag interactions.
- 2Its mechanism is custom transition or animation functions returning CSS or tick behavior for this custom, animations lesson.
- 3Use custom animation only when built-ins cannot express the required motion. Keep decisions specific to custom, animations.
- 4Production code must account for Unbounded tick work or layout reads per frame cause jank. Do not copy assumptions from a neighboring topic into custom, animations.
- 5Teams evaluate it using frame stability measured for custom, animations.
Common Mistakes
- 1Unbounded tick work or layout reads per frame cause jank. Do not copy assumptions from a neighboring topic into custom, animations.
- 2Implementing Custom Animations without understanding custom transition or animation functions returning CSS or tick behavior for this custom, animations lesson.
- 3Choosing Custom Animations where simpler local Svelte code is clearer.
- 4Skipping Profile frame work, interruption, cleanup, and reduced motion. Include an assertion that directly exercises custom, animations.
- 5Optimizing before measuring frame stability measured for custom, animations.
Best Practices
- 1Use custom animation only when built-ins cannot express the required motion. Keep decisions specific to custom, animations.
- 2Document custom transition or animation functions returning CSS or tick behavior for this custom, animations lesson in the smallest useful component, store, action, route, or service.
- 3Represent every relevant loading, success, empty, denied, and failure state.
- 4Profile frame work, interruption, cleanup, and reduced motion. Include an assertion that directly exercises custom, animations.
- 5Use frame stability measured for custom, animations to guide improvements.
How it works
- 1Custom Animations relies on custom transition or animation functions returning CSS or tick behavior for this custom, animations lesson.
- 2Use custom animation only when built-ins cannot express the required motion. Keep decisions specific to custom, animations.
- 3Its main failure mode is Unbounded tick work or layout reads per frame cause jank. Do not copy assumptions from a neighboring topic into custom, animations.
- 4Useful evidence is frame stability measured for custom, animations.
Implementation decisions
- 1Identify the owning component, store, action, route, load function, or server handler.
- 2Keep state local until multiple owners genuinely need it.
- 3Keep server secrets and validation outside browser components.
- 4Define cleanup for subscriptions, actions, timers, and requests.
Verification plan
- 1Profile frame work, interruption, cleanup, and reduced motion. Include an assertion that directly exercises custom, animations.
- 2Check initial render, assignment-driven updates, user interaction, and cleanup.
- 3Confirm keyboard and screen-reader behavior for visible UI.
- 4Measure production output only after correctness passes.
Practice task
- 1Build the smallest Custom Animations example.
- 2Introduce this failure: Unbounded tick work or layout reads per frame cause jank. Do not copy assumptions from a neighboring topic into custom, animations.
- 3Correct it using this rule: Use custom animation only when built-ins cannot express the required motion. Keep decisions specific to custom, animations.
- 4Record frame stability measured for custom, animations before and after the change.
Quick Summary
- Custom Animations works through custom transition or animation functions returning CSS or tick behavior for this custom, animations lesson.
- Use custom animation only when built-ins cannot express the required motion. Keep decisions specific to custom, animations.
- Avoid Unbounded tick work or layout reads per frame cause jank. Do not copy assumptions from a neighboring topic into custom, animations.
- Profile frame work, interruption, cleanup, and reduced motion. Include an assertion that directly exercises custom, animations.
- Measure success with frame stability measured for custom, animations.
Interview Questions
Q1. What is Custom Animations used for?
Answer: It is used for menus, notifications, reordered lists, and drag interactions.
Q2. How does Custom Animations work in Svelte?
Answer: It works through custom transition or animation functions returning CSS or tick behavior for this custom, animations lesson.
Q3. What rule matters most?
Answer: Use custom animation only when built-ins cannot express the required motion. Keep decisions specific to custom, animations.
Q4. What failure is common?
Answer: Unbounded tick work or layout reads per frame cause jank. Do not copy assumptions from a neighboring topic into custom, animations.
Q5. How should it be verified?
Answer: Profile frame work, interruption, cleanup, and reduced motion. Include an assertion that directly exercises custom, animations. Evaluate frame stability measured for custom, animations.
Quiz
Which practice best supports Custom Animations?