Playing Streams with KefirJS

<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>