effect-patterns-scheduling-periodic-tasks

Effect-TS Patterns: Scheduling Periodic Tasks

This skill provides 3 curated Effect-TS patterns for scheduling periodic tasks. Use this skill when working on tasks related to:

• scheduling periodic tasks
• Best practices in Effect-TS applications
• Real-world patterns and solutions

🟡 Intermediate Patterns

Scheduling Pattern 4: Debounce and Throttle Execution

Rule: Use debounce to wait for silence before executing, and throttle to limit execution frequency, both critical for handling rapid events.

Good Example:

This example demonstrates debouncing and throttling for common scenarios.

import { Effect, Schedule, Ref } from "effect";

interface SearchQuery {
  readonly query: string;
  readonly timestamp: Date;
}

// Simulate API search
const performSearch = (query: string): Effect.Effect<string[]> =>
  Effect.gen(function* () {
    yield* Effect.log(`[API] Searching for: "${query}"`);

    yield* Effect.sleep("100 millis"); // Simulate API delay

    return [
      `Result 1 for ${query}`,
      `Result 2 for ${query}`,
      `Result 3 for ${query}`,
    ];
  });

// Main: demonstrate debounce and throttle
const program = Effect.gen(function* () {
  console.log(`\n[DEBOUNCE/THROTTLE] Handling rapid events\n`);

  // Example 1: Debounce search input
  console.log(`[1] Debounced search (wait for silence):\n`);

  const searchQueries = ["h", "he", "hel", "hell", "hello"];

  const debouncedSearches = yield* Ref.make<Effect.Effect<string[]>[]>([]);

  for (const query of searchQueries) {
    yield* Effect.log(`[INPUT] User typed: "${query}"`);

    // In real app, this would be debounced
    yield* Effect.sleep("150 millis"); // User typing
  }

  // After user stops, execute search
  yield* Effect.log(`[DEBOUNCE] User silent for 200ms, executing search`);

  const searchResults = yield* performSearch("hello");

  yield* Effect.log(`[RESULTS] ${searchResults.length} results found\n`);

  // Example 2: Throttle scroll events
  console.log(`[2] Throttled scroll handler (max 10/sec):\n`);

  const scrollEventCount = yield* Ref.make(0);
  const updateCount = yield* Ref.make(0);

  // Simulate 100 rapid scroll events
  for (let i = 0; i < 100; i++) {
    yield* Ref.update(scrollEventCount, (c) => c + 1);

    // In real app, scroll handler would be throttled
    if (i % 10 === 0) {
      // Simulate throttled update (max 10 per second)
      yield* Ref.update(updateCount, (c) => c + 1);
    }
  }

  const events = yield* Ref.get(scrollEventCount);
  const updates = yield* Ref.get(updateCount);

  yield* Effect.log(
    `[THROTTLE] ${events} scroll events → ${updates} updates (${(updates / events * 100).toFixed(1)}% update rate)\n`
  );

  // Example 3: Deduplication
  console.log(`[3] Deduplicating rapid events:\n`);

  const userClicks = ["click", "click", "click", "dblclick", "click"];

  const lastClick = yield* Ref.make<string | null>(null);
  const clickCount = yield* Ref.make(0);

  for (const click of userClicks) {
    const prev = yield* Ref.get(lastClick);

    if (click !== prev) {
      yield* Effect.log(`[CLICK] Processing: ${click}`);
      yield* Ref.update(clickCount, (c) => c + 1);
      yield* Ref.set(lastClick, click);
    } else {
      yield* Effect.log(`[CLICK] Duplicate: ${click} (skipped)`);
    }
  }

  const processed = yield* Ref.get(clickCount);

  yield* Effect.log(
    `\n[DEDUPE] ${userClicks.length} clicks → ${processed} processed\n`
  );

  // Example 4: Exponential backoff on repeated errors
  console.log(`[4] Throttled retry on errors:\n`);

  let retryCount = 0;

  const operation = Effect.gen(function* () {
    retryCount++;

    if (retryCount < 3) {
      yield* Effect.fail(new Error("Still failing"));
    }

    yield* Effect.log(`[SUCCESS] Succeeded on attempt ${retryCount}`);

    return "done";
  }).pipe(
    Effect.retry(
      Schedule.exponential("100 millis").pipe(
        Schedule.upTo("1 second"),
        Schedule.recurs(5)
      )
    )
  );

  yield* operation;
});

Effect.runPromise(program);