Svelte UI Animator

Implement purposeful, performant animations using Svelte's built-in transitions and actions. Focus on key moments: hero intros, hover feedback, content reveals, and navigation transitions with Svelte's reactive nature.

Core Philosophy

"You don't need animations everywhere" - Prioritize:

Workflow

Execute phases sequentially. Complete each before proceeding.

Phase 1: Analyze

1. Scan project structure - Identify all pages in src/routes/ and components in src/lib/components/
2. Check existing setup - Review tailwind.config.js and app.html for existing animations/keyframes
3. Identify animation candidates - List components by priority category
4. Document constraints - Note installed animation libraries (svelte/transition, auto-animate, motion, etc.)

Output: Animation audit table. See references/component-checklist.md.

Phase 2: Plan

1. Map animations to components - Assign specific animation patterns
2. Determine triggers - Load, scroll (intersection), hover, click
3. Estimate effort - Low (CSS only), Medium (hooks needed), High (library required)
4. Propose phased rollout - Quick wins first

Output: Implementation plan with component → animation mapping.

Phase 3: Implement

1. Extend Tailwind config - Add keyframes and animation utilities
2. Add reduced-motion support - Accessibility first
3. Create reusable actions - scrollReveal, mousePosition, staggerAnimate if needed
4. Apply animations per component - Follow patterns in references/animation-patterns.md

Performance rules:

<!-- ✅ DO: Use transforms and opacity only -->
<div style="transform: translateY(20px); opacity: 0.5; filter: blur(4px);" />

<!-- ❌ DON'T: Animate layout properties -->
<div style="margin-top: 20px; height: 100px; width: 200px;" />

Phase 4: Verify

1. Test in browser - Visual QA all animations
2. Test reduced-motion - Verify prefers-reduced-motion works
3. Check CLS - No layout shifts from animations
4. Performance audit - No jank on scroll animations

Quick Reference

Animation Triggers

Common Patterns

Staggered children with Svelte transitions:

<script>
  import { flip, fly } from 'svelte/transition';
</script>

{#each items as item, i (item.id)}
  <div
    in:fly={{ y: 20, delay: i * 50 }}
    out:fly={{ y: -20 }}
  >
    {item.content}
  </div>
{/each}

Advanced scroll reveal action:

<!-- actions/scrollReveal.js -->
export function scrollReveal(node, options = {}) {
  const {
    threshold = 0.1,
    animation = 'fade-slide-up',
    delay = 0
  } = options;

  const observer = new IntersectionObserver(
    ([entry]) => {
      if (entry.isIntersecting) {
        setTimeout(() => {
          node.classList.add('animate-' + animation);
        }, delay);
      }
    },
    { threshold }
  );

  observer.observe(node);

  return {
    destroy() => observer.disconnect()
  };
}

Usage with reactive state:

<script>
  import { scrollReveal } from '$lib/actions/scrollReveal.js';
  import { onMount } from 'svelte';

  let isVisible = false;
  let element;

  onMount(() => {
    const observer = new IntersectionObserver(
      ([entry]) => isVisible = entry.isIntersecting
    );
    observer.observe(element);
    return () => observer.disconnect();
  });
</script>

<div
  bind:this={element}
  use:scrollReveal={{ animation: 'fade-in', delay: 100 }}
  class:visible={isVisible}
>
  Content here
</div>

Resources

• Animation patterns: See references/animation-patterns.md
• Audit template: See references/component-checklist.md
• Tailwind presets: See references/tailwind-presets.md

Technical Stack

• Svelte transitions: Primary choice - fade, fly, slide, scale, blur, crossfade
• CSS animations: For complex keyframe animations not covered by Svelte transitions
• Tailwind utilities: For hover states and basic animations
• Auto-animate: For automatic layout animations (if installed)
• Svelte actions: For custom scroll-triggered and interactive animations
• Motion: For advanced gesture-based animations (if installed)
• GSAP: For timeline-based sequences (if already installed)

Accessibility (Required)

Always include in global CSS:

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}