chromium-bidi 2.1.2: EventEmitter

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 chromium-bidi.EventEmitter in pkg:npm/chromium-bidi@2.1.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/chromium-bidi@2.1.2
Demonstrate these symbols/APIs:
  - chromium-bidi.EventEmitter

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:sha256:2cc04ccb4f4eaa564f01d8b91e9da130f19cc17d5cefb98aed8fca458cc47dc5","contract":["EventEmitter is instantiated with new EventEmitter()","on binds an event listener and receives emitted data payload","multiple event listeners execute in order of registration","once binds a one-time event listener that executes only on the first emit","off removes an event listener so it is not invoked on subsequent emits","removeAllListeners(event) removes listeners for a specific event while preserving other events","removeAllListeners() without arguments clears all listeners for all events","on, once, off, and removeAllListeners return the EventEmitter instance for method chaining"],"goal":"verify chromium-bidi.EventEmitter in pkg:npm/chromium-bidi@2.1.2","kind":"HOW","packages":["pkg:npm/chromium-bidi@2.1.2"],"schemaVersion":1,"symbols":["chromium-bidi.EventEmitter"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"npm","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/chromium-bidi@2.1.2"],"schemaVersion":1,"subject":"pkg:npm/chromium-bidi@2.1.2","symbols":["chromium-bidi.EventEmitter"],"verifierAdapter":"node-typescript@1"}

import { EventEmitter } from 'chromium-bidi/lib/esm/utils/EventEmitter.js';

export function createEventEmitter() {
  return new EventEmitter();
}

export { EventEmitter };

{
  "name": "sample-chromium-bidi-eventemitter",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-chromium-bidi-eventemitter",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "chromium-bidi": "2.1.2"
      }
    },
    "node_modules/chromium-bidi": {
      "version": "2.1.2",
      "resolved": "https://registry.npmjs.org/chromium-bidi/-/chromium-bidi-2.1.2.tgz",
      "integrity": "sha512-vtRWBK2uImo5/W2oG6/cDkkHSm+2t6VHgnj+Rcwhb0pP74OoUb4GipyRX/T/y39gYQPhioP0DPShn+A7P6CHNw==",
      "license": "Apache-2.0",
      "dependencies": {
        "mitt": "^3.0.1",
        "zod": "^3.24.1"
      },
      "peerDependencies": {
        "devtools-protocol": "*"
      }
    },
    "node_modules/devtools-protocol": {
      "version": "0.0.1686980",
      "resolved": "https://registry.npmjs.org/devtools-protocol/-/devtools-protocol-0.0.1686980.tgz",
      "integrity": "sha512-NnnxGO1/cRffXL29DqGysbfgCcsYoIxprtmXgh+UDXFvhTwhRBewcRdGlEXvc3cmROi04JRmd2PqCURsijW25A==",
      "license": "BSD-3-Clause",
      "peer": true
    },
    "node_modules/mitt": {
      "version": "3.0.1",
      "resolved": "https://registry.npmjs.org/mitt/-/mitt-3.0.1.tgz",
      "integrity": "sha512-vKivATfr97l2/QBCYAkXYDbrIWPM2IIKEl7YPhjCvKlG3kE2gm+uBo6nEXK3M5/Ffh/FLpKExzOQ3JJoJGFKBw==",
      "license": "MIT"
    },
    "node_modules/zod": {
      "version": "3.25.76",
      "resolved": "https://registry.npmjs.org/zod/-/zod-3.25.76.tgz",
      "integrity": "sha512-gzUt/qt81nXsFGKIFcC3YnfEAx5NkunCfnDlvuBSSFS02bcXu4Lmea0AFIUwbLWxWPx3d9p8S5QoaujKcNQxcQ==",
      "license": "MIT",
      "funding": {
        "url": "https://github.com/sponsors/colinhacks"
      }
    }
  }
}

{
  "name": "sample-chromium-bidi-eventemitter",
  "version": "1.0.0",
  "private": true,
  "description": "verify chromium-bidi.EventEmitter in pkg:npm/chromium-bidi@2.1.2",
  "type": "module",
  "main": "index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "chromium-bidi": "2.1.2"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify chromium-bidi.EventEmitter in pkg:npm/chromium-bidi@2.1.2",
  "kind": "HOW",
  "packages": [
    "pkg:npm/chromium-bidi@2.1.2"
  ],
  "symbols": [
    "chromium-bidi.EventEmitter"
  ]
}

import assert from 'node:assert';
import { EventEmitter as DirectEventEmitter } from 'chromium-bidi/lib/esm/utils/EventEmitter.js';
import { EventEmitter as BidiMapperEventEmitter } from 'chromium-bidi/lib/esm/bidiMapper/BidiMapper.js';
import { createEventEmitter, EventEmitter } from '../index.mjs';

async function run() {
  // 1. Verify class exports and construction
  assert.strictEqual(typeof EventEmitter, 'function', 'EventEmitter should be exported as a class/function');
  assert.strictEqual(typeof DirectEventEmitter, 'function', 'DirectEventEmitter should be exported as a class/function');
  assert.strictEqual(typeof BidiMapperEventEmitter, 'function', 'BidiMapperEventEmitter should be exported as a class/function');
  assert.strictEqual(EventEmitter, DirectEventEmitter, 'Index EventEmitter should match DirectEventEmitter');
  assert.strictEqual(BidiMapperEventEmitter, DirectEventEmitter, 'BidiMapper EventEmitter should match DirectEventEmitter');

  const emitter = new EventEmitter();
  assert.ok(emitter instanceof EventEmitter, 'emitter should be an instance of EventEmitter');

  const helperEmitter = createEventEmitter();
  assert.ok(helperEmitter instanceof EventEmitter, 'createEventEmitter should return an EventEmitter instance');

  // 2. Test `on` and `emit`
  const receivedMessages = [];
  const onResult = emitter.on('message', (payload) => {
    receivedMessages.push(payload);
  });
  assert.strictEqual(onResult, emitter, 'on() must return the emitter instance for chaining');

  emitter.emit('message', { id: 1, text: 'first' });
  emitter.emit('message', { id: 2, text: 'second' });

  assert.strictEqual(receivedMessages.length, 2, 'Listener should have received two events');
  assert.deepStrictEqual(receivedMessages[0], { id: 1, text: 'first' });
  assert.deepStrictEqual(receivedMessages[1], { id: 2, text: 'second' });

  // 3. Test multiple listeners on same event
  const order = [];
  emitter.on('multi', () => order.push('listener1'));
  emitter.on('multi', () => order.push('listener2'));
  emitter.emit('multi', null);
  assert.deepStrictEqual(order, ['listener1', 'listener2'], 'Listeners must execute in registration order');

  // 4. Test `once`
  const onceMessages = [];
  const onceResult = emitter.once('single', (payload) => {
    onceMessages.push(payload);
  });
  assert.strictEqual(onceResult, emitter, 'once() must return the emitter instance for chaining');

  emitter.emit('single', 'event-1');
  emitter.emit('single', 'event-2');
  emitter.emit('single', 'event-3');

  assert.strictEqual(onceMessages.length, 1, 'once listener must be invoked only once');
  assert.strictEqual(onceMessages[0], 'event-1', 'once listener must receive the first event payload');

  // 5. Test `off`
  const offMessages = [];
  const handlerToRemove = (payload) => {
    offMessages.push(payload);
  };

  emitter.on('removable', handlerToRemove);
  emitter.emit('removable', 'before-off');
  assert.strictEqual(offMessages.length, 1, 'Listener should receive event before off()');

  const offResult = emitter.off('removable', handlerToRemove);
  assert.strictEqual(offResult, emitter, 'off() must return the emitter instance');

  emitter.emit('removable', 'after-off');
  assert.strictEqual(offMessages.length, 1, 'Listener must not receive event after off()');

  // 6. Test `removeAllListeners(event)` for a specific event
  const eventA = [];
  const eventB = [];
  emitter.on('topicA', (val) => eventA.push(val));
  emitter.on('topicB', (val) => eventB.push(val));

  const removeSpecificResult = emitter.removeAllListeners('topicA');
  assert.strictEqual(removeSpecificResult, emitter, 'removeAllListeners(event) must return the emitter instance');

  emitter.emit('topicA', 'should-be-dropped');
  emitter.emit('topicB', 'should-be-received');

  assert.strictEqual(eventA.length, 0, 'topicA listeners should have been removed');
  assert.strictEqual(eventB.length, 1, 'topicB listeners should remain intact');
  assert.strictEqual(eventB[0], 'should-be-received');

  // 7. Test `removeAllListeners()` without arguments
  const eventC = [];
  emitter.on('topicC', (val) => eventC.push(val));

  const removeAllResult = emitter.removeAllListeners();
  assert.strictEqual(removeAllResult, emitter, 'removeAllListeners() must return the emitter instance');

  emitter.emit('topicB', 'dropped-b');
  emitter.emit('topicC', 'dropped-c');

  assert.strictEqual(eventB.length, 1, 'topicB should receive no new events');
  assert.strictEqual(eventC.length, 0, 'topicC should receive no events');

  console.log('Contract tests passed successfully.');
}

run().catch((err) => {
  console.error('Contract test failed:', err);
  process.exit(1);
});