Reactive Bindings

Reactive bindings in kivi are implemented with a simple Invalidator objects, UI Components can subscribe and listen for invalidation signals with methods subscribe and transientSubscribe. The difference between subscriptions and transient subscriptions is that transient subscriptions will be automatically canceled when UI Component is invalidated, so UI Component should resubscribe each time it updates its representation, transient subscriptions are useful when subscriptions may change over time.

Invalidator objects are way much simpler than composable streams, or implicit graphs of data dependencies, they doesn't pass any information except the signal that something is changed. Because all subscriptions are explicit it also has a predictable performance and it is easier to review code.

It was designed to get rid of data changes over time in as much places as possible, so instead of pushing/pulling data from streams, we just reevaluate everything and using caches to prevent from unnecessary computations. This programming model is significantly simpler and provides a better debugging experience, especially when investigating bugs from stack traces in production builds.

const mode: "a" | "b" = "a";
const a = 0;
const b = 0;
const modeInvalidator = new Invalidator();
const aInvalidator = new Invalidator();
const bInvalidator = new Invalidator();

const Main = new ComponentDescriptor<void, void>()
  .attached((c) => {
  .update((c) => {
    let value: number;
    if (mode === "a") {
      value = a;
    } else {
      value = b;

function update() {
  if (mode === "a") {
    if (a === 10) {
      a = 0;
      mode = "b";
  } else {
    if (b === 10) {
      b = 0;
      mode = "a";
  setTimeout(1000, update);
setTimeout(1000, update);

injectComponent(Main, document.body);