Programming Tutorials

  For years, the standard implementation for scroll-linked animations—parallax hero images, reading progress bars, and scroll-triggered fade-ins—has been imperative JavaScript. We attach listeners to the   window , calculate   scrollTop , normalize the value, and imperatively update DOM styles. Even with aggressive throttling, debouncing, or wrapping updates in  requestAnimationFrame , this approach suffers from a fundamental architectural flaw: it binds visual updates to the  Main Thread . On mobile devices with high refresh rate displays (90Hz+), the main thread is often busy parsing HTML, hydrating frameworks like React, or executing third-party scripts. When the main thread hangs, your scroll listener hangs. The result is "jank"—a visual stutter where the scroll momentum (handled by the browser's compositor) desynchronizes from the JavaScript-driven styles. The solution is to decouple scroll animations from JavaScript execution entirely using the CSS Scroll-...