Selector emission scheduling — internal only

Selector scheduler helpers are implementation details. Do not import them from package subpaths or teach consumers to wrap selector readables manually.

Public facade: @themislib/themis/svelte-store (store.createSelector and Store selector options). Selector implementation and scheduler internals are package-private; see @themislib/themis/docs/SELECTORS.md for behavior.

Scheduling options

• Tune Svelte-readable selector coalescing only through the final constructor options argument: new Store(reducers, middleware, { throttledSelectorFrequency }).
• Treat this as Svelte Store family scheduling. Use the Store-owned scheduler rather than adding a second scheduling layer.
• Omit throttledSelectorFrequency for the default 64 FPS; explicit values must be finite numbers in the inclusive 1..256 range. Fractional values are supported.
• Selector trace output is disabled by default; pass { traceSelectors: true } in the final Store options object only for temporary diagnostics.

Scheduling does not change which call mode is valid. Use ../selector-lifecycle/SKILL.md → Call-mode map for components, handlers, services, tests, saga reads, and explicit binding; its Bind explicitly with .withStore when no Svelte context is available section covers initialization and subscription cleanup. Authoring and cache reuse live in ../selectors/SKILL.md → Choose the factory and Selector caching.

Do not

• Do not import selector scheduler internals from app code.
• Do not wrap Store-created selectors, selector callbacks, selector calls, or selector readables in extra memoize, cache, debounce/throttle, timer, requestAnimationFrame, scheduler, or writable-proxy layers just to reduce recomputes or UI updates.
• Do not rely on selector readables as audit/event streams; they represent the latest derived state and may coalesce intermediate writes.
• Respect ../selector-lifecycle/SKILL.md → Don't even when a readable is cached or scheduled.

Examples

Configure coalescing on the Store

import { Store } from "@themislib/themis/svelte-store";
import { pointerReducer } from "./pointer-slice";

export const store = new Store({ pointer: pointerReducer }, [], {
  throttledSelectorFrequency: 30,
});

Define and compose selectors with ../selectors/SKILL.md → Examples; consume them using ../selector-lifecycle/SKILL.md → Examples. The same Store-owned scheduling applies without a custom wrapper or copied call-mode recipe.

6. ❌ Bad: wrapping selector readables in another cache or timer layer

// BAD: this compiles but adds stale updates on top of Store-owned caching/scheduling.
import { writable, type Readable } from "svelte/store";
import { selectPointer } from "./pointer-selectors";

type Pointer = { x: number; y: number };

export function createManuallyDebouncedPointer(): Readable<Pointer> {
  const output = writable<Pointer>({ x: 0, y: 0 });
  selectPointer().subscribe((value) => setTimeout(() => output.set(value), 100));
  return output;
}

7. ❌ Bad: treating selector readables as event logs

// BAD: selector readables represent latest state and may coalesce intermediate writes.
import { selectPointer } from "./pointer-selectors";

type Pointer = { x: number; y: number };

export function recordEveryPointerMove(audit: Pointer[]) {
  const unsubscribe = selectPointer().subscribe((pointer) => audit.push(pointer));
  return unsubscribe;
}

8. Prefer action or saga evidence when every event matters

import { call, takeEvery } from "typed-redux-saga";
import { pointerMoved } from "./pointer-slice";

declare const auditLog: { write(event: string, payload: unknown): Promise<void> };

export function* pointerAuditSaga() {
  yield* takeEvery(pointerMoved, function* auditPointerMove(action) {
    yield* call(auditLog.write, "pointer-moved", action.payload[0]);
  });
}

Verification cues

• FPS values satisfy Scheduling options; default behavior needs no extra scheduler.
• Consumers needing every event use action/saga evidence, not coalesced state readables.
• Validate call sites against ../selector-lifecycle/SKILL.md → Verification cues.

See also

• ../selectors/SKILL.md — building Store-bound selectors and cache contracts.
• ../selector-lifecycle/SKILL.md — selector call-site modes and cleanup.
• @themislib/themis/docs/SELECTORS.md — selector memoization and lifecycle rules.