Why is my page jumping?

A page that seems to jump or jerk while scrolling can be annoying for users. There are a few potential causes for a jumpy page:

Too many animations or transitions

If you have a lot of CSS or JavaScript animations and transitions happening on your page as you scroll, this can sometimes cause a jittery effect. Things like image sliders, auto-playing videos, scrolling parallax effects, lazy loading content, and CSS animations should be used sparingly.

Try to minimize or remove any unnecessary animations. For necessary animations, try optimizing the code to improve performance. Setting animation durations to quicker times (e.g. 0.5s instead of 2s) can also help make things feel smoother.

Heavy images or media files

Large image, video, and audio files that haven’t been optimized properly can also cause a page to stutter while scrolling. Here are a few tips for optimizing media:

• Use image optimization tools to reduce file sizes without sacrificing quality.
• Enable lazy loading for images/videos below the fold.
• Use lighter image formats when possible – JPEG is smaller than PNG for photos.
• Set appropriate video resolutions – not everyone needs 4K!
• Host media on a CDN to improve load times.

Too many fonts or icon fonts

Using too many different fonts and weights downloaded from Google Fonts or other font services can contribute to a choppy scrolling effect. Try to minimize the number of unique fonts in use.

Icon fonts can also be culprits, especially if the page is loading hundreds of icons from a spritesheet. Try using inline SVG or icon images instead.

Complicated CSS effects

Some CSS effects like box shadows, gradients, transparency, and filters can be taxing on browsers to render on long pages. Try simplifying or removing heavy shadows, gradients, and effects if possible.

Also make sure you are using GPU acceleration and browser prefixes to optimize animated CSS effects.

Javascript issues

Badly coded JavaScript running expensive operations on scroll events can also cause jank. Here are some tips for optimizing JS:

• Debounce scroll and resize event listeners.
• Avoid synchronous XMLHttpRequest calls.
• Minimize layout thrashing – read styles before writing.
• Use requestAnimationFrame() for visual changes.
• Throttle/debounce events that fire excessively.

Repaints and reflows

If the browser has to frequently re-render the page while scrolling due to changes in layout, this can cause some jumpiness. To reduce repaints/reflows:

• Avoid setting inline styles frequently.
• Batch DOM changes together.
• Enable will-change if using CSS transforms.
• Promote heavy layers to their own composite layer.

Memory leaks

A memory leak caused by poorly coded JavaScript can also result in jerky scrolling behavior. Watch for any rapid memory buildup in your Chrome Devtools Timeline and diagnose the cause.

Cleanup HTML, CSS, and JS

In general, having lean and optimized code will help improve scrolling performance. Here are some tips:

• Remove any unused JavaScript and CSS code.
• Minify and concatenate CSS/JS files.
• Use HTML5 semantic tags where possible.
• Avoid tag soup – properly structure HTML.
• Remove inline styling and move to CSS classes.

Enable virtualization

For very long lists and tables, enabling virtualization can significantly improve performance. This only renders visible rows/items rather than the full dataset.

Virtualization can be implemented in JavaScript frameworks like React or directly in CSS with libraries like react-window.

Use simpler scroll effects

Most scrolling issues arise from trying to achieve complicated scroll effects like parallax, anchors, and snapping. Try using simpler scroll behavior if you are able:

• Avoid parallax backgrounds.
• Use fewer anchors.
• Don’t manipulate scroll position.

Enabling smooth scrolling and momentum on iOS and other touch devices can also help improve perceived performance.

Check resource loading

Ensure that key resources like CSS and JS files are loading in an optimal way. Leverage protocols like HTTP/2 prioritization and server push.

Also check that render blocking resources are loaded before other requests. Use deferred scripts where possible.

Test on mobile devices

Some scrolling issues may only occur on mobile or touch devices. Be sure to thoroughly test your site’s scrolling performance on both desktop and mobile.

Mobile devices have less memory and slower processors so it’s important that performance is acceptable.

Use profiling tools

Chrome DevTools provides several useful profiling tools to diagnose scrolling issues:

• Performance panel – Evaluate load metrics
• Rendering tab – Find forced reflows
• Memory tab – Detect memory leaks
• Console warnings – Identify bottlenecks

Using profiling consistently can help catch scroll problems early before users notice.

Add GPU acceleration

Enabling GPU acceleration allows the browser to offload some rendering work to the device’s graphics processor. This can significantly boost scrolling speed.

To enable, set transform: translate3d(0,0,0) on animated elements and translateZ(0) on containers with opacity/clip animations.

Reduce layout shifting

Layout shifts from loading content can make scrolling feel jerky. Reduce shifts by:

• Setting heights/widths on images and containers.
• Avoid inserting content above existing content.
• Using animation rather than showing/hiding.
• Enabling text compression.

Improve interactivity

Try to maintain 60fps while scrolling for smoothest feel. During interaction:

• Defer non-critical work with requestIdleCallback().
• Throttle events like scroll and resize.
• Bind touchmove events passively.

Check site speed

Improving overall site speed and Time to Interactive (TTI) metric will provide a smoother scrolling experience:

• Minify HTML/CSS/JS.
• Compress images.
• Preload key requests.
• Reduce redirect hops.
• Remove unused code.

Aim for TTI under 5 seconds on mobile networks.

Conclusion

Fixing a jumpy scrolling page may require tweaking your site’s HTML, CSS, JavaScript, media assets, and general performance. Be meticulous about optimizing code, enable GPU acceleration, minimize layout shifts, and use profiling tools to diagnose the root cause.

Test scrolling thoroughly on both desktop and mobile to ensure a smooth experience for all users. Patience and persistence pays off – keep eliminating potential issues until scrolling feels seamless.