Effective Techniques for Preloading Lottie Animation Frames with CSS

When enhancing website interactivity, animations such as Lottie often bring designs to life. However, ensuring a smooth and seamless user experience—especially during initial interactions—can sometimes be challenging. For developers working on custom implementations, optimizing the preload process for animation frames is crucial to prevent flickering, layout shifts, and delayed loading.

A common approach is attempting to replace Lottie animations with pure CSS snippets, aiming for faster load times and greater control. Yet, one significant hurdle is preloading all the image frames used in the animation, so they are instantly available when triggered.

The Challenge

In a recent project, I set out to recreate a 3D rotating effect on energy cans as a hover interaction, originally built with Webflow and Lottie. Transitioning to an HTML, CSS, and JavaScript solution, I faced a problem: the first hover action causes a flash of all frames loading simultaneously, resulting in visual flickering and unexpected layout shifts.

Despite trying to initiate the animation once on page load via JavaScript, the images still don’t preload as desired, leading to the initial lag.

Why Is Preloading Important?

Preloading assets ensures all images or frames are cached in the browser before the user interacts, leading to smooth animations without interruption. When frames aren’t preloaded, the browser must fetch images on-demand, which causes delays and undesirable visual artifacts.

Approaches Tried

• CSS sprite sheets: Combining frames into a sprite reduces load times but complicates development.
• JavaScript preloading: Programmatically loading all image frames early on to cache them before user interaction.
• Triggering an off-screen animation: Running the animation once during page load to cache frames (which didn’t fully solve the problem).

Practical Recommendations

• Preload All Frames: Use JavaScript to explicitly load each frame image during page initialization. For example:

javascript
const frameCount = 30; // Adjust based on your frames
for (let i = 1; i <= frameCount; i++) {
const img = new Image();
img.src = `path/to/frames/frame${i}.png`;
}

• Use a Hidden Container: Append these images to a hidden container so they are cached without affecting layout.
• Optimize File Sizes: Compress your images to balance quality and loading speed.
• Leverage Web Workers or Lazy Loading: For more advanced setups, consider