scheduler 0.25.0: unstable_cancelCallback

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify unstable_cancelCallback in pkg:npm/scheduler@0.25.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/scheduler@0.25.0
Demonstrate these symbols/APIs:
  - unstable_cancelCallback

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:71b43fd3dea1485960a1809090e049f8e996814d05bc538d9449b4a125518492","contract":["scheduler package exports unstable_cancelCallback as a callable function","unstable_cancelCallback sets the callback of a scheduled task to null","unstable_cancelCallback prevents an immediate or normal priority callback from executing","unstable_cancelCallback cancels delayed scheduled tasks before their delay timer expires","unstable_cancelCallback is idempotent and safely handles already cancelled tasks"],"goal":"verify unstable_cancelCallback in pkg:npm/scheduler@0.25.0","kind":"HOW","packages":["pkg:npm/scheduler@0.25.0"],"schemaVersion":1,"symbols":["unstable_cancelCallback"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/scheduler@0.25.0"],"schemaVersion":1,"subject":"pkg:npm/scheduler@0.25.0","symbols":["unstable_cancelCallback"],"verifierAdapter":"node-typescript@1"}

{
  "name": "verify-scheduler-unstable-cancel-callback",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "verify-scheduler-unstable-cancel-callback",
      "version": "1.0.0",
      "dependencies": {
        "scheduler": "0.25.0"
      }
    },
    "node_modules/scheduler": {
      "version": "0.25.0",
      "resolved": "https://registry.npmjs.org/scheduler/-/scheduler-0.25.0.tgz",
      "integrity": "sha512-xFVuu11jh+xcO7JOAGJNOXld8/TcEHK/4CituBUeUb5hqxJLj9YuemAEuvm9gQ/+pgXYfbQuqAkiYu+u7YEsNA==",
      "license": "MIT"
    }
  }
}

{
  "name": "verify-scheduler-unstable-cancel-callback",
  "version": "1.0.0",
  "private": true,
  "description": "verify unstable_cancelCallback in pkg:npm/scheduler@0.25.0",
  "type": "module",
  "main": "src/index.js",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "scheduler": "0.25.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify unstable_cancelCallback in pkg:npm/scheduler@0.25.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/scheduler@0.25.0"
  ],
  "symbols": [
    "unstable_cancelCallback"
  ]
}

import Scheduler from 'scheduler';

const {
  unstable_scheduleCallback,
  unstable_cancelCallback,
  unstable_ImmediatePriority,
  unstable_UserBlockingPriority,
  unstable_NormalPriority,
  unstable_LowPriority,
  unstable_IdlePriority,
  unstable_now,
} = Scheduler;

/**
 * Schedules a callback with the given priority level and options.
 *
 * @param {number} priorityLevel - Priority level (1=Immediate, 2=UserBlocking, 3=Normal, 4=Low, 5=Idle)
 * @param {Function} callback - Task callback function
 * @param {object} [options] - Options object, e.g. { delay: number }
 * @returns {object} Scheduled task node
 */
export function scheduleTask(priorityLevel, callback, options) {
  return unstable_scheduleCallback(priorityLevel, callback, options);
}

/**
 * Cancels a scheduled task node by clearing its callback reference.
 *
 * @param {object} task - Task node returned by scheduleTask / unstable_scheduleCallback
 */
export function cancelTask(task) {
  return unstable_cancelCallback(task);
}

export {
  unstable_scheduleCallback,
  unstable_cancelCallback,
  unstable_ImmediatePriority,
  unstable_UserBlockingPriority,
  unstable_NormalPriority,
  unstable_LowPriority,
  unstable_IdlePriority,
  unstable_now,
};

import assert from 'node:assert/strict';
import Scheduler, {
  unstable_cancelCallback,
  unstable_scheduleCallback,
  unstable_ImmediatePriority,
  unstable_UserBlockingPriority,
  unstable_NormalPriority,
  unstable_LowPriority,
  unstable_IdlePriority,
  unstable_now,
} from 'scheduler';
import {
  scheduleTask,
  cancelTask,
} from '../src/index.js';

// Contract 1: scheduler package exports unstable_cancelCallback as a callable function
{
  assert.strictEqual(typeof unstable_cancelCallback, 'function');
  assert.strictEqual(typeof Scheduler.unstable_cancelCallback, 'function');
  assert.strictEqual(unstable_cancelCallback, Scheduler.unstable_cancelCallback);
  assert.strictEqual(typeof cancelTask, 'function');
}

// Contract 2: unstable_cancelCallback sets the callback of a scheduled task to null
{
  const callbackFn = () => {};
  const task = scheduleTask(unstable_NormalPriority, callbackFn);
  assert.strictEqual(task.callback, callbackFn);
  cancelTask(task);
  assert.strictEqual(task.callback, null);
}

// Contract 3: unstable_cancelCallback prevents an immediate or normal priority callback from executing
await new Promise((resolve, reject) => {
  let executedNormal = false;
  let executedKept = false;

  const cancelledTask = scheduleTask(unstable_NormalPriority, () => {
    executedNormal = true;
  });

  const keptTask = scheduleTask(unstable_NormalPriority, () => {
    executedKept = true;
  });

  cancelTask(cancelledTask);

  setTimeout(() => {
    try {
      assert.strictEqual(executedNormal, false, 'Cancelled task should not execute');
      assert.strictEqual(executedKept, true, 'Uncancelled task should execute');
      resolve();
    } catch (err) {
      reject(err);
    }
  }, 50);
});

// Contract 4: unstable_cancelCallback cancels delayed scheduled tasks before their delay timer expires
await new Promise((resolve, reject) => {
  let executedDelayed = false;

  const delayedTask = scheduleTask(
    unstable_LowPriority,
    () => {
      executedDelayed = true;
    },
    { delay: 20 }
  );

  assert.ok(delayedTask.startTime > 0);
  assert.strictEqual(typeof delayedTask.callback, 'function');
  cancelTask(delayedTask);
  assert.strictEqual(delayedTask.callback, null);

  setTimeout(() => {
    try {
      assert.strictEqual(executedDelayed, false, 'Cancelled delayed task should not execute');
      resolve();
    } catch (err) {
      reject(err);
    }
  }, 60);
});

// Contract 5: unstable_cancelCallback is idempotent and safely handles already cancelled tasks
{
  const task = scheduleTask(unstable_IdlePriority, () => {});
  cancelTask(task);
  assert.strictEqual(task.callback, null);
  assert.doesNotThrow(() => {
    cancelTask(task);
  });
  assert.strictEqual(task.callback, null);
}

console.log('All contract assertions passed successfully.');