RXJS - Only emit bigger values than the last value

index.js

const { rxObserver } = require('api/v0.3');
const { timer, from, of, EMPTY } = require('rxjs');
const { zip, startWith, pairwise, switchMap } = require('rxjs/operators');


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


// compare values pairwise
const result$ = source$.pipe(
  startWith(-1),
  pairwise(),
  switchMap(([a,b])=>
    b > a
    ? of(b)
    : EMPTY
  )
);

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