interval

A tick event driven by your own start/stop events, with a per-scope "running" flag.

const { tick, active } = interval({ ms, start, stop, leading });
// tick: Event<void>   active: Store<boolean>

A game or session timer

import { interval } from "@virentia/core/utils";

const enteredGame = event<void>();
const leftGame = event<void>();

const { tick, active } = interval({ ms: 1000, start: enteredGame, stop: leftGame });

reaction({ on: tick, run: () => { elapsed.value += 1; } });

active is readable state, not bookkeeping — bind a pause indicator or a pulsing dot straight to it.

Polling while a screen is open

Tie the lifetime to route events and refresh on every tick:

const { tick } = interval({ ms: 15_000, start: ordersOpened, stop: ordersClosed, leading: true });

reaction({ on: tick, run: () => void refreshOrdersFx() });

leading: true fires the first tick immediately on start — the screen loads data right away, then keeps it fresh. Check refreshOrdersFx.pending.value in the reaction if the network can be slower than the interval, so refreshes don't stack.

Autosave every N seconds while editing

const { tick } = interval({ ms: 30_000, start: editingStarted, stop: editingStopped });

reaction({ on: tick, run: () => void saveDraftFx(draft.value) });

For "save after the user pauses" prefer debounce; interval is for "save on the clock, no matter what".

When to reach for it

• Timers, stopwatches, countdowns visible to the user.
• Polling with a lifetime owned by the model (route opened/closed), not by a component's mount.
• Recurring background work while some mode is on: autosave, presence pings, token refresh.

Behaviour notes

• Per scope. start in one scope ticks only that scope; active is true only there. Two tests never share a timer.
• start while running is a no-op — it does not reset the phase and cannot double-schedule.
• Owner dispose stops every scope and sets active back to false — no orphan timers after unmount.
• Ticks are new root updates; failures in reactions on tick are reported per the error contract and do not stop the interval.