Scroll Reveal Libraries

Overview

This skill covers AOS (Animate On Scroll), a lightweight CSS-driven library for scroll-triggered animations. AOS excels at simple fade, slide, and zoom effects activated when elements enter the viewport.

Key Features:

Minimal Setup: Single JavaScript file + CSS
Data Attribute API: Configure animations in HTML
Performance: CSS-driven, GPU-accelerated animations
50+ Built-in Animations: Fades, slides, zooms, flips
Framework Agnostic: Works with vanilla JS, React, Vue, etc.

When to Use:

Marketing/landing pages with simple scroll effects
Content-heavy sites (blogs, documentation)
Quick prototypes requiring scroll animations
Projects where GSAP/Framer Motion complexity isn't needed

When NOT to Use:

Complex animation timelines or orchestration → Use GSAP ScrollTrigger
Physics-based animations → Use React Spring or Framer Motion
Precise scroll-synced animations → Use GSAP ScrollTrigger
Heavy interactive animations → Use Framer Motion

Core Concepts

Installation

CDN (Quickest):

<head>
  <link rel="stylesheet" href="https://unpkg.com/aos@next/dist/aos.css" />
</head>
<body>
  <!-- Content with data-aos attributes -->

  <script src="https://unpkg.com/aos@next/dist/aos.js"></script>
  <script>
    AOS.init();
  </script>
</body>

NPM/Yarn (Recommended):

npm install aos@next
# or
yarn add aos@next

import AOS from 'aos';
import 'aos/dist/aos.css';

AOS.init();

Basic Usage

Apply animations using the data-aos attribute:

<!-- Fade in -->
<div data-aos="fade-in">Content</div>

<!-- Fade up -->
<div data-aos="fade-up">Content</div>

<!-- Slide from right -->
<div data-aos="slide-left">Content</div>

<!-- Zoom in -->
<div data-aos="zoom-in">Content</div>

Configuration Options

Global Configuration:

AOS.init({
  // Animation settings
  duration: 800,  // Animation duration (ms): 0-3000
  delay: 0,       // Delay before animation (ms): 0-3000
  offset: 120,    // Offset from trigger point (px)
  easing: 'ease', // Easing function
  once: false,    // Animate only once (true) or every time (false)
  mirror: false,  // Animate out when scrolling past

  // Placement
  anchorPlacement: 'top-bottom', // Which position triggers animation

  // Performance
  disable: false,                // Disable on mobile/tablet
  startEvent: 'DOMContentLoaded', // Initialization event
  debounceDelay: 50,             // Window resize debounce
  throttleDelay: 99              // Scroll throttle
});

Per-Element Overrides:

<div
  data-aos="fade-up"
  data-aos-duration="1000"
  data-aos-delay="200"
  data-aos-offset="50"
  data-aos-easing="ease-in-out"
  data-aos-once="true"
  data-aos-mirror="true"
  data-aos-anchor-placement="center-bottom"
>
  Custom configured element
</div>

Common Patterns

1. Landing Page Hero Section

<section class="hero">
  <!-- Staggered heading words -->
  <h1
    data-aos="fade-down"
    data-aos-duration="800"
  >
    Welcome to the Future
  </h1>

  <!-- Delayed subheading -->
  <p
    data-aos="fade-up"
    data-aos-delay="200"
    data-aos-duration="600"
  >
    Transform your ideas into reality
  </p>

  <!-- CTA button -->
  <button
    data-aos="zoom-in"
    data-aos-delay="400"
    data-aos-duration="500"
  >
    Get Started
  </button>
</section>

2. Feature Cards Grid

<div class="features-grid">
  <!-- Stagger cards with increasing delays -->
  <div
    class="feature-card"
    data-aos="fade-up"
    data-aos-duration="600"
    data-aos-delay="0"
  >
    <h3>Feature 1</h3>
    <p>Description...</p>
  </div>

  <div
    class="feature-card"
    data-aos="fade-up"
    data-aos-duration="600"
    data-aos-delay="100"
  >
    <h3>Feature 2</h3>
    <p>Description...</p>
  </div>

  <div
    class="feature-card"
    data-aos="fade-up"
    data-aos-duration="600"
    data-aos-delay="200"
  >
    <h3>Feature 3</h3>
    <p>Description...</p>
  </div>
</div>

3. Alternating Content Sections

<!-- Content from left -->
<div class="section">
  <div
    class="content"
    data-aos="slide-right"
    data-aos-duration="800"
  >
    <h2>Section Title</h2>
    <p>Content slides in from left...</p>
  </div>
  <img
    src="image1.jpg"
    data-aos="fade-left"
    data-aos-delay="200"
  />
</div>

<!-- Content from right -->
<div class="section reverse">
  <img
    src="image2.jpg"
    data-aos="fade-right"
  />
  <div
    class="content"
    data-aos="slide-left"
    data-aos-duration="800"
    data-aos-delay="200"
  >
    <h2>Section Title</h2>
    <p>Content slides in from right...</p>
  </div>
</div>

4. Scroll-Triggered Testimonials

<div class="testimonials">
  <div
    class="testimonial"
    data-aos="zoom-in"
    data-aos-duration="500"
  >
    <blockquote>"Amazing product!"</blockquote>
    <cite>- John Doe</cite>
  </div>

  <div
    class="testimonial"
    data-aos="zoom-in"
    data-aos-duration="500"
    data-aos-delay="100"
  >
    <blockquote>"Exceeded expectations"</blockquote>
    <cite>- Jane Smith</cite>
  </div>
</div>

5. Custom Anchor Triggers

Trigger animations based on a different element's scroll position:

<!-- Fixed sidebar animates based on main content scroll -->
<div class="main-content">
  <div id="trigger-point" data-aos-id="sidebar-trigger">
    <!-- Content -->
  </div>
</div>

<aside
  class="sidebar"
  data-aos="fade-left"
  data-aos-anchor="#trigger-point"
>
  Sidebar content
</aside>

6. Sequential Animation Chain

<div class="animation-sequence">
  <!-- Step 1: Heading -->
  <h2
    data-aos="fade-down"
    data-aos-duration="600"
    data-aos-delay="0"
  >
    Our Process
  </h2>

  <!-- Step 2: Description -->
  <p
    data-aos="fade-up"
    data-aos-duration="600"
    data-aos-delay="200"
  >
    Follow these simple steps
  </p>

  <!-- Step 3-5: Process cards -->
  <div
    class="process-step"
    data-aos="flip-left"
    data-aos-delay="400"
  >
    Step 1
  </div>

  <div
    class="process-step"
    data-aos="flip-left"
    data-aos-delay="600"
  >
    Step 2
  </div>

  <div
    class="process-step"
    data-aos="flip-left"
    data-aos-delay="800"
  >
    Step 3
  </div>
</div>

7. Image Gallery with Zoom Effects

<div class="gallery">
  <img
    src="photo1.jpg"
    data-aos="zoom-in-up"
    data-aos-duration="800"
  />
  <img
    src="photo2.jpg"
    data-aos="zoom-in-up"
    data-aos-duration="800"
    data-aos-delay="100"
  />
  <img
    src="photo3.jpg"
    data-aos="zoom-in-up"
    data-aos-duration="800"
    data-aos-delay="200"
  />
</div>

Integration Patterns

React Integration

Basic Setup:

import { useEffect } from 'react';
import AOS from 'aos';
import 'aos/dist/aos.css';

function App() {
  useEffect(() => {
    AOS.init({
      duration: 800,
      once: true,
      offset: 100
    });
  }, []);

  return (
    <div>
      <h1 data-aos="fade-down">Welcome</h1>
      <p data-aos="fade-up">Content here</p>
    </div>
  );
}

Refreshing on Route Changes:

import { useEffect } from 'react';
import { useLocation } from 'react-router-dom';
import AOS from 'aos';

function App() {
  const location = useLocation();

  useEffect(() => {
    AOS.init({ duration: 800 });
  }, []);

  // Refresh AOS on route change
  useEffect(() => {
    AOS.refresh();
  }, [location]);

  return <Routes>{/* routes */}</Routes>;
}

Dynamic Content Updates:

import { useState, useEffect } from 'react';
import AOS from 'aos';

function DynamicList() {
  const [items, setItems] = useState([]);

  useEffect(() => {
    AOS.init();
  }, []);

  const addItem = () => {
    setItems([...items, { id: Date.now(), text: 'New Item' }]);

    // Refresh AOS to detect new elements
    setTimeout(() => AOS.refresh(), 50);
  };

  return (
    <div>
      <button onClick={addItem}>Add Item</button>
      <ul>
        {items.map((item) => (
          <li key={item.id} data-aos="fade-in">
            {item.text}
          </li>
        ))}
      </ul>
    </div>
  );
}

Component Wrapper Pattern:

import AOS from 'aos';
import 'aos/dist/aos.css';

function AnimatedSection({ children, animation = "fade-up", delay = 0, ...props }) {
  return (
    <div
      data-aos={animation}
      data-aos-delay={delay}
      {...props}
    >
      {children}
    </div>
  );
}

// Usage
<AnimatedSection animation="slide-right" delay={200}>
  <h2>Animated Content</h2>
</AnimatedSection>

Vue.js Integration

<template>
  <div>
    <h1 data-aos="fade-down">Vue + AOS</h1>
    <div
      v-for="(item, index) in items"
      :key="item.id"
      data-aos="fade-up"
      :data-aos-delay="index * 100"
    >
      {{ item.text }}
    </div>
  </div>
</template>

<script>
import AOS from 'aos';
import 'aos/dist/aos.css';

export default {
  mounted() {
    AOS.init({ duration: 800 });
  },
  updated() {
    // Refresh when component updates
    this.$nextTick(() => {
      AOS.refresh();
    });
  },
  data() {
    return {
      items: [/*...*/]
    };
  }
};
</script>

Next.js Integration

// pages/_app.js
import { useEffect } from 'react';
import AOS from 'aos';
import 'aos/dist/aos.css';

function MyApp({ Component, pageProps }) {
  useEffect(() => {
    AOS.init({
      duration: 800,
      once: true
    });
  }, []);

  return <Component {...pageProps} />;
}

export default MyApp;

// pages/index.js
export default function Home() {
  return (
    <main>
      <h1 data-aos="fade-down">Next.js + AOS</h1>
      <p data-aos="fade-up">Server-side rendered content with animations</p>
    </main>
  );
}

Performance Optimization

1. Disable on Mobile Devices

AOS.init({
  disable: 'mobile', // Disable on mobile
  // Or use function for custom logic
  disable: function() {
    return window.innerWidth < 768;
  }
});

2. Use Once for Better Performance

AOS.init({
  once: true, // Animate only once (better performance)
  mirror: false // Don't animate out
});

3. Optimize Throttle and Debounce

AOS.init({
  throttleDelay: 99,  // Scroll event throttle (default)
  debounceDelay: 50   // Resize event debounce (default)
});

4. Disable Mutation Observer for Static Content

AOS.init({
  disableMutationObserver: true // Disable for fully static content
});

5. Reduce Animation Complexity

<!-- Simpler animations perform better -->
<div data-aos="fade-in">Simple fade</div>

<!-- Complex animations may cause jank -->
<div data-aos="flip-left">Complex flip</div>

6. Use RequestIdleCallback for Initialization

if ('requestIdleCallback' in window) {
  requestIdleCallback(() => {
    AOS.init({ duration: 800 });
  });
} else {
  AOS.init({ duration: 800 });
}

Common Pitfalls

1. Forgetting to Refresh After DOM Changes

Problem: New elements don't animate after being added dynamically.

Solution: Call AOS.refresh() or AOS.refreshHard():

// After adding elements to DOM
const newElement = document.createElement('div');
newElement.setAttribute('data-aos', 'fade-in');
container.appendChild(newElement);

// Refresh AOS
AOS.refresh(); // Recalculate positions
// or
AOS.refreshHard(); // Reinitialize completely

2. Animations Not Working in React

Problem: AOS doesn't detect elements on first render or route changes.

Solution: Initialize in useEffect and refresh on route/content changes:

useEffect(() => {
  AOS.init();
  return () => AOS.refresh(); // Cleanup
}, []);

useEffect(() => {
  AOS.refresh(); // Refresh on route change
}, [location.pathname]);

3. Scroll Performance Issues

Problem: Page scrolling feels janky with many animated elements.

Solution: Reduce animated elements and use once: true:

AOS.init({
  once: true, // Animate only once
  disable: window.innerWidth < 768 // Disable on mobile
});

4. CSS Conflicts

Problem: Custom CSS interferes with AOS animations.

Solution: Use more specific selectors and avoid !important:

/* Bad: Conflicts with AOS */
div {
  opacity: 1 !important;
}

/* Good: Specific selector */
.my-content > div {
  /* styles */
}

5. Anchor Placement Confusion

Problem: Animations trigger at unexpected scroll positions.

Solution: Understand anchor placement options:

// Triggers when element's top hits viewport bottom
data-aos-anchor-placement="top-bottom"

// Triggers when element's center hits viewport center
data-aos-anchor-placement="center-center"

// Triggers when element's bottom hits viewport top
data-aos-anchor-placement="bottom-top"

6. Duration/Delay Limits

Problem: Values above 3000ms don't work.

Solution: Add custom CSS for extended durations:

body[data-aos-duration='4000'] [data-aos],
[data-aos][data-aos][data-aos-duration='4000'] {
  transition-duration: 4000ms;
}

<div data-aos="fade-in" data-aos-duration="4000">
  Long animation
</div>

Built-in Animations

Fade Animations

fade-in - Simple fade in
fade-up - Fade in from bottom
fade-down - Fade in from top
fade-left - Fade in from right
fade-right - Fade in from left
fade-up-right - Diagonal fade
fade-up-left - Diagonal fade
fade-down-right - Diagonal fade
fade-down-left - Diagonal fade

Slide Animations

slide-up - Slide from bottom
slide-down - Slide from top
slide-left - Slide from right
slide-right - Slide from left

Zoom Animations

zoom-in - Zoom in
zoom-in-up - Zoom in from bottom
zoom-in-down - Zoom in from top
zoom-in-left - Zoom in from right
zoom-in-right - Zoom in from left
zoom-out - Zoom out
zoom-out-up - Zoom out to top
zoom-out-down - Zoom out to bottom
zoom-out-left - Zoom out to left
zoom-out-right - Zoom out to right

Flip Animations

flip-up - Flip from bottom
flip-down - Flip from top
flip-left - Flip from right
flip-right - Flip from left

Custom Animations

Create custom animations with CSS:

[data-aos="custom-slide-bounce"] {
  opacity: 0;
  transform: translateY(100px);
  transition-property: transform, opacity;
}

[data-aos="custom-slide-bounce"].aos-animate {
  opacity: 1;
  transform: translateY(0);
  animation: bounce 0.5s;
}

@keyframes bounce {
  0%, 20%, 50%, 80%, 100% {
    transform: translateY(0);
  }
  40% {
    transform: translateY(-10px);
  }
  60% {
    transform: translateY(-5px);
  }
}

<div data-aos="custom-slide-bounce">
  Custom animation
</div>

Comparison with Alternatives

AOS vs GSAP ScrollTrigger

Feature	AOS	GSAP ScrollTrigger
Complexity	Simple, data-attribute based	Advanced, JavaScript API
Use Case	Simple reveals	Complex timelines
File Size	~13KB	~27KB (GSAP) + ScrollTrigger
Performance	CSS-driven	JavaScript-driven
Learning Curve	Minutes	Hours
Customization	Limited	Extensive
Best For	Marketing pages	Interactive experiences

Use AOS when:

Simple fade/slide/zoom effects
Quick implementation needed
Minimal JavaScript preferred
Basic scroll reveals sufficient

Use GSAP ScrollTrigger when:

Complex animation sequences
Precise scroll-synced animations
Timeline orchestration needed
Advanced easing/physics required

Resources

Official Documentation

AOS: https://michalsnik.github.io/aos/
GitHub: https://github.com/michalsnik/aos

Key Scripts

scripts/aos_generator.py - Generate AOS HTML boilerplate
scripts/config_builder.py - Build AOS configuration

References

references/aos_api.md - Complete AOS API reference
references/animation_catalog.md - All built-in animations with demos
references/integration_patterns.md - Framework integration guides

Starter Assets

assets/starter_aos/ - Complete AOS starter template
assets/examples/ - Production-ready patterns

Related Skills

gsap-scrolltrigger: For complex scroll-driven animations
motion-framer: For React-specific animations with physics
locomotive-scroll: For smooth scrolling with parallax
animated-component-libraries: For pre-built animated React components

scroll-reveal-libraries

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SKILL.md

Scroll Reveal Libraries

Overview

Core Concepts

Installation

Basic Usage

Configuration Options

Common Patterns

1. Landing Page Hero Section

2. Feature Cards Grid

3. Alternating Content Sections

4. Scroll-Triggered Testimonials

5. Custom Anchor Triggers

6. Sequential Animation Chain

7. Image Gallery with Zoom Effects

Integration Patterns

React Integration

Vue.js Integration

Next.js Integration

Performance Optimization

1. Disable on Mobile Devices

2. Use Once for Better Performance

3. Optimize Throttle and Debounce

4. Disable Mutation Observer for Static Content

5. Reduce Animation Complexity

6. Use RequestIdleCallback for Initialization

Common Pitfalls

1. Forgetting to Refresh After DOM Changes

2. Animations Not Working in React

3. Scroll Performance Issues

4. CSS Conflicts

5. Anchor Placement Confusion

6. Duration/Delay Limits

Built-in Animations

Fade Animations

Slide Animations

Zoom Animations

Flip Animations

Custom Animations

Comparison with Alternatives

AOS vs GSAP ScrollTrigger

Resources

Official Documentation

Key Scripts

References

Starter Assets

Related Skills