ms 2.0.0: format millisecond durations to short or verbose strings and parse duration strings with ms

# ms Duration Formatting and Parsing

## Overview
`ms` provides conversion between human-readable duration strings (e.g. `'2 days'`, `'1d'`, `'10h'`, `'1m'`, `'5s'`) and millisecond integers, as well as formatting millisecond counts into either concise strings (e.g. `'1m'`, `'1d'`) or verbose strings (e.g. `'1 minute'`, `'2 minutes'`, `'1 day'`).

## Parsing Behavior
1. Parses time units: `milliseconds`, `seconds`, `minutes`, `hours`, `days`, `years` and their abbreviations (`ms`, `s`, `m`, `h`, `d`, `y`).
2. Suffixless strings (e.g. `'100'`) default to milliseconds.
3. Unrecognized unit strings (e.g. `'invalid'`) return `undefined` rather than throwing.
4. Empty strings, invalid numbers, or non-string/non-number values throw an explicit Error.

## Formatting Behavior
1. Default format (`ms(n)`): Returns compact strings such as `'500ms'`, `'1m'`, `'2m'`, `'1d'`.
2. Long format (`ms(n, { long: true })`): Returns pluralized strings such as `'1 minute'`, `'2 minutes'`, `'1 day'`, `'2 days'`.

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: format millisecond durations to short or verbose strings and parse duration strings with ms
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/ms@2.0.0
Demonstrate these symbols/APIs:
  - ms

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:sha256:8d4cc317034a11f9cb580d1be369a1f88f5de1be2143fefc1907a712864fb304","contract":["assert.strictEqual(ms('2 days'), 172800000);","assert.strictEqual(ms('1d'), 86400000);","assert.strictEqual(ms('10h'), 36000000);","assert.strictEqual(ms('2.5 hrs'), 9000000);","assert.strictEqual(ms('1m'), 60000);","assert.strictEqual(ms('5s'), 5000);","assert.strictEqual(ms('100'), 100);","assert.strictEqual(ms('100ms'), 100);","assert.strictEqual(ms('1y'), 31557600000);","assert.strictEqual(ms(60000), '1m');","assert.strictEqual(ms(2 * 60000), '2m');","assert.strictEqual(ms(86400000), '1d');","assert.strictEqual(ms(500), '500ms');","assert.strictEqual(ms(60000, { long: true }), '1 minute');","assert.strictEqual(ms(2 * 60000, { long: true }), '2 minutes');","assert.strictEqual(ms(86400000, { long: true }), '1 day');","assert.strictEqual(ms(2 * 86400000, { long: true }), '2 days');","assert.strictEqual(ms('invalid'), undefined);","assert.throws(() =\u003e ms(''), /val is not a non-empty string or a valid number/);"],"goal":"format millisecond durations to short or verbose strings and parse duration strings with ms","kind":"HOW","packages":["pkg:npm/ms@2.0.0"],"schemaVersion":1,"symbols":["ms"]},"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/ms@2.0.0"],"schemaVersion":1,"subject":"pkg:npm/ms@2.0.0","symbols":["ms"],"verifierAdapter":"node-typescript@1"}

{
  "name": "ms-format-and-parse-durations",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "ms-format-and-parse-durations",
      "version": "1.0.0",
      "dependencies": {
        "ms": "2.0.0"
      }
    },
    "node_modules/ms": {
      "version": "2.0.0",
      "resolved": "https://registry.npmjs.org/ms/-/ms-2.0.0.tgz",
      "integrity": "sha512-Tpp60P6IUJDTuOq/5Z8cdskzJujfwqfOTkrwIwj7IRISpnkJnT6SyJ4PCPnGMoFjC9ddhal5KVIYtAt97ix05A==",
      "license": "MIT"
    }
  }
}

{
  "name": "ms-format-and-parse-durations",
  "version": "1.0.0",
  "type": "module",
  "dependencies": {
    "ms": "2.0.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "format millisecond durations to short or verbose strings and parse duration strings with ms",
  "kind": "HOW",
  "packages": [
    "pkg:npm/ms@2.0.0"
  ],
  "symbols": [
    "ms"
  ]
}

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

// 1. Parsing duration strings into milliseconds
assert.strictEqual(ms('2 days'), 172800000);
assert.strictEqual(ms('1d'), 86400000);
assert.strictEqual(ms('10h'), 36000000);
assert.strictEqual(ms('2.5 hrs'), 9000000);
assert.strictEqual(ms('1m'), 60000);
assert.strictEqual(ms('5s'), 5000);
assert.strictEqual(ms('100'), 100);
assert.strictEqual(ms('100ms'), 100);
assert.strictEqual(ms('1y'), 31557600000);

// 2. Formatting milliseconds into short duration strings
assert.strictEqual(ms(60000), '1m');
assert.strictEqual(ms(2 * 60000), '2m');
assert.strictEqual(ms(86400000), '1d');
assert.strictEqual(ms(500), '500ms');

// 3. Formatting milliseconds into verbose/long duration strings
assert.strictEqual(ms(60000, { long: true }), '1 minute');
assert.strictEqual(ms(2 * 60000, { long: true }), '2 minutes');
assert.strictEqual(ms(86400000, { long: true }), '1 day');
assert.strictEqual(ms(2 * 86400000, { long: true }), '2 days');

// 4. Invalid inputs: unrecognized string returns undefined; empty input or non-number throws
assert.strictEqual(ms('invalid'), undefined);
assert.throws(() => ms(''), /val is not a non-empty string or a valid number/);