Using array of observable functions with each items output being the next items input

index.js

const { rxObserver, palette } = require('api/v0.3');
const { of } = require('rxjs');
const { switchMap, delay} = require('rxjs/operators');

const fns =
  [ (value) => of(value + 1).pipe(delay(100))
  , (value) => of(value + 3).pipe(delay(100))
  , (value) => of(value + 5).pipe(delay(100))
  ]

fns.reduce(
  (acc, fn) => acc.pipe( switchMap(fn) ) // switchMap to next fn result
  , of(0)                                // initial value to pass to the first fn
)
  .subscribe(rxObserver())