Kefir is a lighter alernative to RxJS.
Here is a simple counter in functional reactive programming.
You can play with it here kefirCounter
<script
src="https://cdnjs.cloudflare.com/ajax/libs/kefir/3.8.0/kefir.min.js" >
</script>
<button id="inc">+</button>
<span id="result">0</span>
<button id="dec">-</button>
<script>
/****************** Helpers **********************/
const elt = (id) => document.getElementById(id);
const fromEvts = Kefir.fromEvents;
const merge = Kefir.merge;
const clickEvt = "click";
const ident = (v) => () => v;
const one = ident(1);
const negone = ident(-1);
const add = (x, y) => x + y;
/*************************************************/
const inc$ =
fromEvts(elt("inc"), clickEvt)
.map(one);
const dec$ =
fromEvts(elt("dec"), clickEvt)
.map(negone);
const sum$ =
merge([inc$, dec$])
.scan(add, 0)
.onValue(s => result.innerText = s);
</script>
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