[RxJS] Adding Conditional Logic with Filter

Often you only want values to proceed through your stream if they meet certain criteria, just as if you were using an

if

statement in plain JavaScript. This lesson shows you how to use

filter

on your stream to only push the values that you need through your stream.

const Observable = Rx.Observable;

const startButton = document.querySelector('#start');
const halfButton = document.querySelector('#half');
const quarterButton = document.querySelector('#quarter');

const stopButton = document.querySelector('#stop');
const resetButton = document.querySelector('#reset');

const input = document.querySelector('#input');

const start$ = Observable.fromEvent(startButton, 'click');
const half$ = Observable.fromEvent(halfButton, 'click');
const quarter$ = Observable.fromEvent(quarterButton, 'click');

const stop$ = Observable.fromEvent(stopButton, 'click');
const reset$ = Observable.fromEvent(resetButton, 'click');

const input$ = Observable.fromEvent(input, 'input')
.map(event => event.target.value);

const data = {count:0};
const inc = (acc)=> ({count: acc.count + 1});
const reset = (acc)=> data;

const starters$ = Observable.merge(
start$.mapTo(1000),
half$.mapTo(500),
quarter$.mapTo(250)
);

const intervalActions = (time)=> Observable.merge(
Observable.interval(time)
.takeUntil(stop$).mapTo(inc),
reset$.mapTo(reset)
);

const timer$ = starters$
.switchMap(intervalActions)
.startWith(data)
.scan((acc, curr)=> curr(acc))

Observable.combineLatest(
timer$,
input$,
(timer, input)=> ({count: timer.count, text: input})
)
.filter((data)=> data.count === parseInt(data.text))
.subscribe(
(x)=> console.log(x),
err=> console.log(err),
()=> console.log('complete')
);