https://stackoverflow.com/questions/55758934/rxjs-only-emit-bigger-values-than-the-last-value/55772042 **alternative**

index.js

const { rxObserver } = require('api/v0.3');
const { timer, from, of, EMPTY } = require('rxjs');
const { zip, debounceTime, map, scan, distinctUntilChanged } = require('rxjs/operators');

// create a source using values
const values$ = from([ 5, 10, 20, 10, 5, 20, 0, 5, 30 ]);
const source$ = timer(0, 10).pipe(
  zip(values$, (_,x)=>x)
);


const result$ = source$.pipe(
  map(e => e),
  scan((prev, curr) => Math.max(prev, curr), 0),
  distinctUntilChanged()
);

source$.subscribe(rxObserver('source$'));
result$.subscribe(rxObserver('result$'));