Window-scroll-manager NPM

Window Scroll Manager

Small library that broadcasts more performant window-scroll events.

What is this?

Listening to window onscroll event is very expensive and ineffective, so this library tries to get better performance out of it.

Implementation is simple - it listens to window scroll event, but broadcasts custom window-scroll event once one per requestAnimationFrame. By my benchmarks it behaves much better.

If your event handler is doing any repaint logic, consider doing the logic it in requestAnimationFrame.

Idea came from MDN, but I tried to take it one step further by making this singleton scroll manager. It will use passive events if browser supports them.

One note for Safari, negative scroll values will be returned as 0.

Usage

Get it from npm:

npm install window-scroll-manager

Import it and use it:

import ScrollManager from 'window-scroll-manager'

const sm = new ScrollManager();

console.log(sm.getScrollPosition());
// -> { scrollPositionX: 0, scrollPositionY: 0 }

window.addEventListener('window-scroll', function(e) {
  console.log('Vertical scroll position is: ' + e.detail.scrollPositionY);
  console.log('Horizontal scroll position is: ' + e.detail.scrollPositionX);

  requestAnimationFrame(function() {
    // repaint logic goes here
    // example:
    // rotateDiv.style.transform = 'rotate(' + e.detail.scrollPositionY / 2 + 'deg)';
  });
});

API

getScrollPosition() - returns current window scroll position object.
```
{
  scrollPositionX: 0,
  scrollPositionY: 100,
}
```
removeListener() - reduces internal reference counter by one, and if it reaches 0 destroys the instance. Reference counter is increased every time new ScrollManager is called. For example, this is useful when scroll manager is used in React high order component (to track if any component is still using it). Use with caution.
destroy() - destroys the singleton instance and removes scroll listener. Use with caution, call removeListener do this for you.