I am digging to rxjs and this seems strange to me, here is an example from the rxjs docs, I tried replacing combineLatest with forkJoin and it doesn't work (The subscriber function isn't called), I believe it should because we already kickstarted the obeservables with startsWith(0)
import { fromEvent, combineLatest, forkJoin } from "rxjs";
import { mapTo, startWith, scan, tap, map } from "rxjs/operators";
// elem refs
const redTotal = document.getElementById("red-total");
const blackTotal = document.getElementById("black-total");
const total = document.getElementById("total");
const addOneClick$ = (id) =>
fromEvent(document.getElementById(id), "click").pipe(
// map every click to 1
mapTo(1),
// keep a running total
scan((acc, curr) => acc + curr, 0),
startWith(0)
);
combineLatest(addOneClick$("red"), addOneClick$("black")).subscribe(
([red, black]) => {
redTotal.innerHTML = red;
blackTotal.innerHTML = black;
total.innerHTML = red + black;
console.log(red, black);
}
);<!DOCTYPE html>
<html>
<head>
<title>Parcel Sandbox</title>
<meta charset="UTF-8" />
</head>
<body>
<div>
<button id="red">Red</button>
<button id="black">Black</button>
</div>
<div>Red: <span id="red-total"></span></div>
<div>Black: <span id="black-total"></span></div>
<div>Total: <span id="total"></span></div>
<script src="src/index.js">
</script>
</body>
</html>combineLatest() starts emitting once every observable emits one value. forkJoin() starts emitting once every observable is completed. fromEvent() does not send a complete signal, so that is why using forkJoin() doesn't emit anything.