mitt 3.0.1

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/mitt@3.0.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/mitt@3.0.1

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:sha256:22fd7dac744386f5053bda107b7e670d95c2c25e6fa996b59c607740a9cf610e","contract":["mitt instantiates an event emitter with an all Map and on, off, emit methods","emitter.on registers an event handler that receives emitted payloads","emitter.off removes a specific event handler so subsequent emits do not call it","emitter.off with no handler argument clears all handlers for that event type","emitter.on with wildcard '*' registers a handler receiving event name and payload for any emitted event","mitt accepts an existing Map as the initial event handler storage"],"goal":"verify pkg:npm/mitt@3.0.1","kind":"HOW","packages":["pkg:npm/mitt@3.0.1"],"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","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/mitt@3.0.1"],"schemaVersion":1,"subject":"pkg:npm/mitt@3.0.1","verifierAdapter":"node-typescript@1"}

{
  "name": "sample-mitt",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-mitt",
      "version": "1.0.0",
      "dependencies": {
        "mitt": "3.0.1"
      }
    },
    "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"
    }
  }
}

{
  "name": "sample-mitt",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "dependencies": {
    "mitt": "3.0.1"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/mitt@3.0.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/mitt@3.0.1"
  ]
}

import assert from 'node:assert/strict';
import mitt from 'mitt';

// 1. mitt instantiates an event emitter with an all Map and on, off, emit methods
{
  const emitter = mitt();
  assert.ok(emitter);
  assert.ok(emitter.all instanceof Map);
  assert.equal(typeof emitter.on, 'function');
  assert.equal(typeof emitter.off, 'function');
  assert.equal(typeof emitter.emit, 'function');
}

// 2. emitter.on registers an event handler that receives emitted payloads
{
  const emitter = mitt();
  const received = [];
  emitter.on('foo', (evt) => {
    received.push(evt);
  });

  emitter.emit('foo', { value: 42 });
  emitter.emit('foo', { value: 100 });
  assert.deepEqual(received, [{ value: 42 }, { value: 100 }]);
}

// 3. emitter.off removes a specific event handler so subsequent emits do not call it
{
  const emitter = mitt();
  let callCount = 0;
  const handler = () => {
    callCount++;
  };

  emitter.on('event', handler);
  emitter.emit('event');
  assert.equal(callCount, 1);

  emitter.off('event', handler);
  emitter.emit('event');
  assert.equal(callCount, 1);
}

// 4. emitter.off with no handler argument clears all handlers for that event type
{
  const emitter = mitt();
  let countA = 0;
  let countB = 0;

  emitter.on('multi', () => {
    countA++;
  });
  emitter.on('multi', () => {
    countB++;
  });

  emitter.emit('multi');
  assert.equal(countA, 1);
  assert.equal(countB, 1);

  emitter.off('multi');
  emitter.emit('multi');
  assert.equal(countA, 1);
  assert.equal(countB, 1);
}

// 5. emitter.on with wildcard '*' registers a handler receiving event name and payload for any emitted event
{
  const emitter = mitt();
  const wildcards = [];

  emitter.on('*', (type, evt) => {
    wildcards.push({ type, evt });
  });

  emitter.emit('event1', 'payload1');
  emitter.emit('event2', 123);

  assert.deepEqual(wildcards, [
    { type: 'event1', evt: 'payload1' },
    { type: 'event2', evt: 123 },
  ]);
}

// 6. mitt accepts an existing Map as the initial event handler storage
{
  const initialMap = new Map();
  const handled = [];
  initialMap.set('custom', [(evt) => handled.push(evt)]);

  const emitter = mitt(initialMap);
  emitter.emit('custom', 'init-test');
  assert.deepEqual(handled, ['init-test']);
}