mitt 3.0.1: emitter.off

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 emitter.off in pkg:npm/mitt@3.0.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/mitt@3.0.1
Demonstrate these symbols/APIs:
  - emitter.off
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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:sha256:4d5478d186ff5d5b44d55ffd7b97232ae3183d2840cd5d6ba57d724b04b52f1a","constraints":{"executionContext":"node"},"contract":["emitter.off removes a specific event handler registered with emitter.on","emitter.off called without a handler argument removes all handlers for the specified event type","emitter.off on an event type with no handlers or an unregistered handler is a safe no-op","emitter.off removes only the first matching handler when the same function is registered multiple times","emitter.off removes a specific wildcard handler or clears all wildcard handlers when called with '*'"],"goal":"verify emitter.off in pkg:npm/mitt@3.0.1","kind":"HOW","packages":["pkg:npm/mitt@3.0.1"],"schemaVersion":1,"symbols":["emitter.off"]},"contractCommand":["node","test/contract.mjs"],"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/mitt@3.0.1"],"schemaVersion":1,"subject":"pkg:npm/mitt@3.0.1","symbols":["emitter.off"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-mitt-emitter-off",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-mitt-emitter-off",
      "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-emitter-off",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "dependencies": {
    "mitt": "3.0.1"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify emitter.off in pkg:npm/mitt@3.0.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/mitt@3.0.1"
  ],
  "symbols": [
    "emitter.off"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

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

// 1. emitter.off removes a specific event handler registered with emitter.on
{
  const emitter = mitt();
  const calls = [];
  const handlerA = (data) => calls.push(`A:${data}`);
  const handlerB = (data) => calls.push(`B:${data}`);

  emitter.on('msg', handlerA);
  emitter.on('msg', handlerB);

  emitter.emit('msg', 'first');
  assert.deepEqual(calls, ['A:first', 'B:first']);

  // Remove only handlerA
  emitter.off('msg', handlerA);

  emitter.emit('msg', 'second');
  assert.deepEqual(calls, ['A:first', 'B:first', 'B:second']);
}

// 2. emitter.off called without a handler argument removes all handlers for the specified event type
{
  const emitter = mitt();
  let count = 0;
  emitter.on('ping', () => count++);
  emitter.on('ping', () => count++);

  emitter.emit('ping');
  assert.equal(count, 2);

  // Calling off with only event type clears all handlers for 'ping'
  emitter.off('ping');

  emitter.emit('ping');
  assert.equal(count, 2);
}

// 3. emitter.off on an event type with no handlers or an unregistered handler is a safe no-op
{
  const emitter = mitt();
  const unattachedHandler = () => {};

  // Calling off on non-existent event
  assert.doesNotThrow(() => {
    emitter.off('nonexistent', unattachedHandler);
    emitter.off('nonexistent');
  });

  // Calling off with a handler not in registered list
  let called = false;
  const attachedHandler = () => { called = true; };
  emitter.on('event', attachedHandler);
  assert.doesNotThrow(() => {
    emitter.off('event', unattachedHandler);
  });
  emitter.emit('event');
  assert.equal(called, true);
}

// 4. emitter.off removes only the first matching handler when the same function is registered multiple times
{
  const emitter = mitt();
  let callCount = 0;
  const duplicateHandler = () => callCount++;

  emitter.on('repeat', duplicateHandler);
  emitter.on('repeat', duplicateHandler);

  emitter.emit('repeat');
  assert.equal(callCount, 2);

  // Removes one instance of duplicateHandler
  emitter.off('repeat', duplicateHandler);

  emitter.emit('repeat');
  assert.equal(callCount, 3);

  // Removes the second instance
  emitter.off('repeat', duplicateHandler);

  emitter.emit('repeat');
  assert.equal(callCount, 3);
}

// 5. emitter.off removes a specific wildcard handler or clears all wildcard handlers when called with '*'
{
  const emitter = mitt();
  const wildcards = [];
  const wildA = (type, val) => wildcards.push(`A:${type}:${val}`);
  const wildB = (type, val) => wildcards.push(`B:${type}:${val}`);

  emitter.on('*', wildA);
  emitter.on('*', wildB);

  emitter.emit('event1', 'data1');
  assert.deepEqual(wildcards, ['A:event1:data1', 'B:event1:data1']);

  // Remove specific wildcard handler
  emitter.off('*', wildA);
  emitter.emit('event2', 'data2');
  assert.deepEqual(wildcards, ['A:event1:data1', 'B:event1:data1', 'B:event2:data2']);

  // Clear all remaining wildcard handlers
  emitter.off('*');
  emitter.emit('event3', 'data3');
  assert.deepEqual(wildcards, ['A:event1:data1', 'B:event1:data1', 'B:event2:data2']);
}