merge2 1.4.1

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/merge2@1.4.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/merge2@1.4.1
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:ac2ac4dbc54552de1ee3b259f56be01060828ce84f059ec31b802623a3f7c622","constraints":{"executionContext":"node"},"contract":["merge2 merges multiple readable streams sequentially in order by default","merge2 merges streams concurrently when passed as an array","merge2 dynamically queues additional streams via add method","merge2 emits queueDrain event when all queued streams have completed","merge2 forwards errors from source streams to the merged stream when pipeError option is enabled","merge2 respects end: false option keeping the merged stream open after input streams finish","merge2 throws an error when attempting to merge a non-readable object"],"goal":"verify pkg:npm/merge2@1.4.1","kind":"HOW","packages":["pkg:npm/merge2@1.4.1"],"schemaVersion":1},"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/merge2@1.4.1"],"schemaVersion":1,"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-merge2",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-merge2",
      "version": "1.0.0",
      "dependencies": {
        "merge2": "1.4.1"
      }
    },
    "node_modules/merge2": {
      "version": "1.4.1",
      "resolved": "https://registry.npmjs.org/merge2/-/merge2-1.4.1.tgz",
      "integrity": "sha512-8q7VEgMJW4J8tcfVPy8g09NcQwZdbwFEqhe/WZkoIzjn/3TGDwtOCYtXGxA3O8tPzpczCCDgv+P2P5y00ZJOOg==",
      "license": "MIT",
      "engines": {
        "node": ">= 8"
      }
    }
  }
}

{
  "name": "sample-merge2",
  "version": "1.0.0",
  "type": "module",
  "private": true,
  "dependencies": {
    "merge2": "1.4.1"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/merge2@1.4.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/merge2@1.4.1"
  ],
  "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 { Readable } from 'node:stream';
import merge2 from 'merge2';

function streamFromArray(items, delayMs = 0) {
  let index = 0;
  return new Readable({
    objectMode: true,
    read() {
      if (index >= items.length) {
        this.push(null);
        return;
      }
      const item = items[index++];
      if (delayMs > 0) {
        setTimeout(() => this.push(item), delayMs);
      } else {
        this.push(item);
      }
    }
  });
}

async function collectStream(stream) {
  const result = [];
  for await (const chunk of stream) {
    result.push(chunk);
  }
  return result;
}

// 1. merge2 merges multiple readable streams sequentially in order by default
{
  const s1 = streamFromArray(['a', 'b']);
  const s2 = streamFromArray(['c', 'd']);
  const merged = merge2(s1, s2);
  const results = await collectStream(merged);
  assert.deepEqual(results, ['a', 'b', 'c', 'd']);
}

// 2. merge2 merges streams concurrently when passed as an array
{
  const s1 = streamFromArray(['x1', 'x2'], 20);
  const s2 = streamFromArray(['y1', 'y2'], 5);
  const merged = merge2([s1, s2]);
  const results = await collectStream(merged);
  assert.equal(results.length, 4);
  assert(results.includes('x1') && results.includes('x2') && results.includes('y1') && results.includes('y2'));
}

// 3. merge2 dynamically queues additional streams via .add() method
{
  const s1 = streamFromArray(['first']);
  const merged = merge2(s1);
  const s2 = streamFromArray(['second']);
  merged.add(s2);
  const results = await collectStream(merged);
  assert.deepEqual(results, ['first', 'second']);
}

// 4. merge2 emits queueDrain event when all queued streams have completed
{
  let drained = false;
  const s1 = streamFromArray([1, 2]);
  const merged = merge2(s1);
  merged.on('queueDrain', () => {
    drained = true;
  });
  await collectStream(merged);
  assert.equal(drained, true);
}

// 5. merge2 forwards errors from source streams to the merged stream when pipeError option is enabled
{
  const errStream = new Readable({
    objectMode: true,
    read() {
      this.destroy(new Error('source failure'));
    }
  });
  const merged = merge2(errStream, { pipeError: true });
  let caughtError = null;
  merged.on('error', (err) => {
    caughtError = err;
  });
  try {
    for await (const _ of merged) {}
  } catch (err) {
    caughtError = err;
  }
  assert(caughtError instanceof Error);
  assert.equal(caughtError.message, 'source failure');
}

// 6. merge2 respects end: false option keeping the merged stream open after input streams finish
{
  const s1 = streamFromArray(['part1']);
  const merged = merge2(s1, { end: false });
  const received = [];
  merged.on('data', (chunk) => received.push(chunk));

  await new Promise((resolve) => setTimeout(resolve, 50));
  assert.deepEqual(received, ['part1']);
  assert.equal(merged.readableEnded, false);

  const s2 = streamFromArray(['part2']);
  merged.add(s2);
  await new Promise((resolve) => setTimeout(resolve, 50));
  assert.deepEqual(received, ['part1', 'part2']);
  merged.end();
}

// 7. merge2 throws an error when attempting to merge a non-readable object
{
  assert.throws(
    () => {
      merge2(['not-a-stream']);
    },
    (err) => {
      return err instanceof Error && /Only readable stream can be merged/.test(err.message);
    }
  );
}

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