Fast, Flexible Virtual Scrolling With Functional Programming

Virtual scrolling is a technique where only the visible elements in a list are rendered, improving performance by reducing the number of items loaded into the DOM at any given time.

Virtual scrolling is beneficial for large lists because it improves initial page load time and scrolling performance by rendering only the elements currently in view, rather than all elements at once.

To implement virtual scrolling, you need to compute the total height of rendered elements, determine which elements should be rendered based on the scroll position, and calculate the alignment of these elements within the viewport.

For lists with variable element heights, you compute the cumulative sum of item heights and use it to find the start and end indices for rendering, rather than using basic division.

Optimizations include memoizing intermediate values, using binary search for index calculations, delaying the rendering of non-essential parts, and reusing a pool of list elements to avoid unnecessary DOM manipulation.

The limitation is that un-rendered elements don't appear in browser searches or accessibility tools like screen readers, requiring alternative solutions such as implementing a search bar or using new web standards like CSS content visibility.

CSS content visibility allows elements outside the viewport to be skipped in rendering while still being part of the DOM and accessibility tree, enhancing searchability and accessibility without affecting performance.

A downside is that all elements must still be constructed in the DOM initially, which can be slow, making it less suitable for lists with many small items compared to virtual scrolling.

You can use a pool of reusable elements to avoid creating new elements, instead shifting the contents of these elements as needed, which reduces the need for constant DOM updates.

Using a buffer by rendering extra elements before and after the viewport helps absorb latency during fast scrolling, reducing flickering and improving user experience.