import { fromEvent } from 'rxjs';
import { throttleTime, tap } from 'rxjs/operators';
const scrollIndication = document.getElementById('indication');
const getScrollWidth = () => {
const doc = document.documentElement;
// https://www.w3schools.com/howto/howto_js_scroll_indicator.asp
const winScroll = doc.scrollTop;
const height = doc.scrollHeight - doc.clientHeight;
return (winScroll / height) * 100;
const setScroll = _ => (scrollIndication.style.width = getScrollWidth() + '%');
fromEvent(document, 'scroll')
.pipe(throttleTime(20), tap(setScroll))