events-universal 1.0.1

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 pkg:npm/events-universal@1.0.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/events-universal@1.0.1

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:cfca1c43f1831b21bd148195984dd2415cc9e32ff86ed31eaaea7a767b7dd009","contract":["events-universal exports an EventEmitter constructor","EventEmitter instances register and trigger event listeners with arguments via on and emit","EventEmitter.once registers one-time event listeners that automatically unregister after invocation","EventEmitter.removeListener and off remove specific registered listeners","EventEmitter.removeAllListeners removes all listeners for a given event or all events","EventEmitter.listenerCount returns the number of registered listeners for an event","EventEmitter.eventNames returns an array of registered event names","EventEmitter.prependListener adds listeners to the beginning of the listener array"],"goal":"verify pkg:npm/events-universal@1.0.1","kind":"HOW","packages":["pkg:npm/events-universal@1.0.1"],"schemaVersion":1},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/events-universal@1.0.1"],"schemaVersion":1,"subject":"pkg:npm/events-universal@1.0.1","verifierAdapter":"node-typescript@1"}

{
  "name": "sample-events-universal",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-events-universal",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "events-universal": "1.0.1"
      }
    },
    "node_modules/bare-events": {
      "version": "2.9.1",
      "resolved": "https://registry.npmjs.org/bare-events/-/bare-events-2.9.1.tgz",
      "integrity": "sha512-Z0oHEHAFDZkffN8Qc39zNZjQlMDkPJRyyyZieU1VH7u8c5S+qHZ2S8ixdKIAxEjfHO7FJxXmJWgteOghVanIsg==",
      "license": "Apache-2.0",
      "peerDependencies": {
        "bare-abort-controller": "*"
      },
      "peerDependenciesMeta": {
        "bare-abort-controller": {
          "optional": true
        }
      }
    },
    "node_modules/events-universal": {
      "version": "1.0.1",
      "resolved": "https://registry.npmjs.org/events-universal/-/events-universal-1.0.1.tgz",
      "integrity": "sha512-LUd5euvbMLpwOF8m6ivPCbhQeSiYVNb8Vs0fQ8QjXo0JTkEHpz8pxdQf0gStltaPpw0Cca8b39KxvK9cfKRiAw==",
      "license": "Apache-2.0",
      "dependencies": {
        "bare-events": "^2.7.0"
      }
    }
  }
}

{
  "name": "sample-events-universal",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room code sample for events-universal@1.0.1",
  "license": "MIT-0",
  "dependencies": {
    "events-universal": "1.0.1"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/events-universal@1.0.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/events-universal@1.0.1"
  ]
}

import assert from 'node:assert/strict';
import EventEmitter from 'events-universal';

// 1. events-universal exports an EventEmitter constructor
assert.equal(typeof EventEmitter, 'function', 'EventEmitter export should be a constructor function');
assert.equal(EventEmitter.EventEmitter, EventEmitter, 'EventEmitter.EventEmitter should reference itself');

// 2. EventEmitter instances register and trigger event listeners with arguments via on and emit
const emitter = new EventEmitter();
const receivedArgs = [];
emitter.on('data', (a, b) => {
  receivedArgs.push([a, b]);
});
const emitResult = emitter.emit('data', 'hello', 42);
assert.equal(emitResult, true, 'emit should return true when listeners exist');
assert.deepEqual(receivedArgs, [['hello', 42]], 'listener should receive passed arguments');

// 3. EventEmitter.once registers one-time event listeners that automatically unregister after invocation
let onceCount = 0;
emitter.once('single', (val) => {
  onceCount += val;
});
emitter.emit('single', 10);
emitter.emit('single', 20);
assert.equal(onceCount, 10, 'once listener should execute exactly once');

// 4. EventEmitter.removeListener and off remove specific registered listeners
let removedCalls = 0;
const listenerToRemove = () => {
  removedCalls++;
};
emitter.on('remove-test', listenerToRemove);
emitter.emit('remove-test');
assert.equal(removedCalls, 1, 'listener should be called before removal');
emitter.removeListener('remove-test', listenerToRemove);
emitter.emit('remove-test');
assert.equal(removedCalls, 1, 'listener should not be called after removeListener');

emitter.on('off-test', listenerToRemove);
emitter.off('off-test', listenerToRemove);
emitter.emit('off-test');
assert.equal(removedCalls, 1, 'off should alias removeListener');

// 5. EventEmitter.removeAllListeners removes all listeners for a given event or all events
let countA = 0;
let countB = 0;
emitter.on('evt-a', () => countA++);
emitter.on('evt-a', () => countA++);
emitter.on('evt-b', () => countB++);
emitter.removeAllListeners('evt-a');
emitter.emit('evt-a');
emitter.emit('evt-b');
assert.equal(countA, 0, 'removeAllListeners should remove all listeners for evt-a');
assert.equal(countB, 1, 'evt-b listener should remain intact');
emitter.removeAllListeners();
emitter.emit('evt-b');
assert.equal(countB, 1, 'removeAllListeners without args should remove all listeners across all events');

// 6. EventEmitter.listenerCount returns the number of registered listeners for an event
const countEmitter = new EventEmitter();
assert.equal(countEmitter.listenerCount('ping'), 0, 'initial listenerCount should be 0');
const noop1 = () => {};
const noop2 = () => {};
countEmitter.on('ping', noop1);
assert.equal(countEmitter.listenerCount('ping'), 1, 'listenerCount should be 1 after one registration');
countEmitter.on('ping', noop2);
assert.equal(countEmitter.listenerCount('ping'), 2, 'listenerCount should be 2 after second registration');

// 7. EventEmitter.eventNames returns an array of registered event names
const namesEmitter = new EventEmitter();
assert.deepEqual(namesEmitter.eventNames(), [], 'eventNames should be empty initially');
namesEmitter.on('first', noop1);
namesEmitter.on('second', noop2);
assert.deepEqual(namesEmitter.eventNames().sort(), ['first', 'second'].sort(), 'eventNames should return registered events');

// 8. EventEmitter.prependListener adds listeners to the beginning of the listener array
const orderEmitter = new EventEmitter();
const executionOrder = [];
orderEmitter.on('order', () => executionOrder.push('second'));
orderEmitter.prependListener('order', () => executionOrder.push('first'));
orderEmitter.emit('order');
assert.deepEqual(executionOrder, ['first', 'second'], 'prependListener should execute before previously registered listeners');

console.log('All events-universal contract assertions passed.');