@socket.io/component-emitter 3.1.2

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/%40socket.io/component-emitter@3.1.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40socket.io/component-emitter@3.1.2

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:sha256:49784ae231f1991777e441eee673327e9319864b904339093993ae760d8001c1","contract":["Emitter instance supports event registration and chaining with on and addEventListener","emit and emitReserved dispatch variadic arguments to registered listeners","once listener executes only once and unregisters itself before invocation","off, removeListener, and removeEventListener unregister matching single listeners","off and removeAllListeners with event or no arguments clear listeners","hasListeners and listeners return active listeners array and boolean status","Emitter constructor invoked without new or as mixin enhances target object"],"goal":"verify pkg:npm/%40socket.io/component-emitter@3.1.2","kind":"HOW","packages":["pkg:npm/%40socket.io/component-emitter@3.1.2"],"schemaVersion":1},"contractCommand":["node","test/contract.js"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/%40socket.io/component-emitter@3.1.2"],"schemaVersion":1,"subject":"pkg:npm/%40socket.io/component-emitter@3.1.2","verifierAdapter":"node-typescript@1"}

{
  "name": "sample-component-emitter-contract",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-component-emitter-contract",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "@socket.io/component-emitter": "3.1.2"
      }
    },
    "node_modules/@socket.io/component-emitter": {
      "version": "3.1.2",
      "resolved": "https://registry.npmjs.org/@socket.io/component-emitter/-/component-emitter-3.1.2.tgz",
      "integrity": "sha512-9BCxFwvbGg/RsZK9tjXd8s4UcwR0MWeFQ1XEKIQVVvAGJyINdrqKMcTRyLoK8Rse1GjzLV9cwjWV1olXRWEXVA==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-component-emitter-contract",
  "version": "1.0.0",
  "private": true,
  "description": "Comprehensive contract verification sample for @socket.io/component-emitter",
  "main": "src/index.js",
  "scripts": {
    "test": "node test/contract.js"
  },
  "dependencies": {
    "@socket.io/component-emitter": "3.1.2"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/%40socket.io/component-emitter@3.1.2",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40socket.io/component-emitter@3.1.2"
  ]
}

const { Emitter } = require('@socket.io/component-emitter');

function createEventEmitter() {
  return new Emitter();
}

function mixinEmitter(target) {
  return Emitter(target);
}

module.exports = {
  createEventEmitter,
  mixinEmitter,
  Emitter,
};

const assert = require('node:assert');
const { Emitter } = require('@socket.io/component-emitter');
const { createEventEmitter, mixinEmitter } = require('../src/index.js');

function testChainingAndAliases() {
  const emitter = createEventEmitter();
  const logs = [];

  const ret = emitter
    .on('ping', (msg) => logs.push(`on:${msg}`))
    .addEventListener('ping', (msg) => logs.push(`alias:${msg}`));

  assert.strictEqual(ret, emitter, 'on() should return emitter instance for chaining');

  emitter.emit('ping', 'payload');
  assert.deepStrictEqual(logs, ['on:payload', 'alias:payload'], 'Both on and addEventListener receive events');
}

function testVariadicEmit() {
  const emitter = new Emitter();
  let receivedArgs = null;

  emitter.on('multi', (...args) => {
    receivedArgs = args;
  });

  emitter.emit('multi', 1, 'text', { key: 'value' }, [true, false]);
  assert.deepStrictEqual(receivedArgs, [1, 'text', { key: 'value' }, [true, false]]);

  let reservedArgs = null;
  emitter.on('reserved', (a, b) => {
    reservedArgs = [a, b];
  });
  emitter.emitReserved('reserved', 'alpha', 'beta');
  assert.deepStrictEqual(reservedArgs, ['alpha', 'beta'], 'emitReserved should dispatch identical arguments');
}

function testOnceExecution() {
  const emitter = createEventEmitter();
  let count = 0;

  emitter.once('login', (username) => {
    count += 1;
    assert.strictEqual(username, 'alice');
  });

  emitter.emit('login', 'alice');
  emitter.emit('login', 'alice');
  emitter.emit('login', 'alice');

  assert.strictEqual(count, 1, 'once handler should execute exactly once');
  assert.strictEqual(emitter.hasListeners('login'), false, 'listener should be removed after first emit');
}

function testSelectiveOffAndAliases() {
  const emitter = new Emitter();
  const handled = [];

  const h1 = () => handled.push('h1');
  const h2 = () => handled.push('h2');
  const h3 = () => handled.push('h3');

  emitter.on('event', h1);
  emitter.on('event', h2);
  emitter.on('event', h3);

  emitter.removeListener('event', h2);
  emitter.emit('event');
  assert.deepStrictEqual(handled, ['h1', 'h3']);

  emitter.removeEventListener('event', h1);
  handled.length = 0;
  emitter.emit('event');
  assert.deepStrictEqual(handled, ['h3']);
}

function testRemoveAllListeners() {
  const emitter = new Emitter();
  let calls = 0;
  const fn = () => { calls += 1; };

  emitter.on('ev1', fn);
  emitter.on('ev1', fn);
  emitter.on('ev2', fn);

  emitter.removeAllListeners('ev1');
  assert.strictEqual(emitter.hasListeners('ev1'), false);
  assert.strictEqual(emitter.hasListeners('ev2'), true);

  emitter.removeAllListeners();
  assert.strictEqual(emitter.hasListeners('ev2'), false);

  emitter.emit('ev1');
  emitter.emit('ev2');
  assert.strictEqual(calls, 0);
}

function testStateQueries() {
  const emitter = createEventEmitter();
  assert.strictEqual(emitter.hasListeners('query'), false);
  assert.deepStrictEqual(emitter.listeners('query'), []);

  const fn = () => {};
  emitter.on('query', fn);

  assert.strictEqual(emitter.hasListeners('query'), true);
  assert.deepStrictEqual(emitter.listeners('query'), [fn]);

  emitter.off('query', fn);
  assert.strictEqual(emitter.hasListeners('query'), false);
  assert.deepStrictEqual(emitter.listeners('query'), []);
}

function testMixinApplication() {
  const customService = {
    name: 'OrderService',
    processOrder(id) {
      this.emit('processed', id);
    },
  };

  mixinEmitter(customService);

  let processedId = null;
  customService.on('processed', (id) => {
    processedId = id;
  });

  customService.processOrder('ORD-12345');
  assert.strictEqual(processedId, 'ORD-12345', 'Mixin should equip plain objects with EventEmitter methods');
}

function runContract() {
  testChainingAndAliases();
  testVariadicEmit();
  testOnceExecution();
  testSelectiveOffAndAliases();
  testRemoveAllListeners();
  testStateQueries();
  testMixinApplication();
  console.log('All @socket.io/component-emitter contract assertions passed successfully.');
}

runContract();