levn 0.4.1: parse

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 levn.parse in pkg:npm/levn@0.4.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/levn@0.4.1
Demonstrate these symbols/APIs:
  - levn.parse

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:sha256:25e15e631172911c86d8d9c1cfbbad4f754284f6f1ae8f3de6fd7061b7139a55","contract":["levn.parse parses primitive types including Number, String, Boolean, Undefined, Null, and NaN from string notation","levn.parse parses composite types including arrays, tuples, and objects with nested type specifications","levn.parse parses special types including Date literals and RegExp patterns with optional delimiters and flags","levn.parse parses union types by attempting candidate type conversions in left-to-right precedence order","levn.parse supports explicit mode using wildcard type or explicit option to require unambiguous literal syntax","levn.parse supports custom type definitions with custom typeOf, validate, and cast functions","levn.parse throws an error when the input string does not conform to the expected type"],"goal":"verify levn.parse in pkg:npm/levn@0.4.1","kind":"HOW","packages":["pkg:npm/levn@0.4.1"],"schemaVersion":1,"symbols":["levn.parse"]},"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","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/levn@0.4.1"],"schemaVersion":1,"subject":"pkg:npm/levn@0.4.1","symbols":["levn.parse"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-levn",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-levn",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "levn": "0.4.1"
      }
    },
    "node_modules/levn": {
      "version": "0.4.1",
      "resolved": "https://registry.npmjs.org/levn/-/levn-0.4.1.tgz",
      "integrity": "sha512-+bT2uH4E5LGE7h/n3evcS/sQlJXCpIp6ym8OWJ5eV6+67Dsql/LaaT7qJBAt2rzfoa/5QBGBhxDix1dMt2kQKQ==",
      "license": "MIT",
      "dependencies": {
        "prelude-ls": "^1.2.1",
        "type-check": "~0.4.0"
      },
      "engines": {
        "node": ">= 0.8.0"
      }
    },
    "node_modules/prelude-ls": {
      "version": "1.2.1",
      "resolved": "https://registry.npmjs.org/prelude-ls/-/prelude-ls-1.2.1.tgz",
      "integrity": "sha512-vkcDPrRZo1QZLbn5RLGPpg/WmIQ65qoWWhcGKf/b5eplkkarX0m9z8ppCat4mlOqUsWpyNuYgO3VRyrYHSzX5g==",
      "license": "MIT",
      "engines": {
        "node": ">= 0.8.0"
      }
    },
    "node_modules/type-check": {
      "version": "0.4.0",
      "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.4.0.tgz",
      "integrity": "sha512-XleUoc9uwGXqjWwXaUTZAmzMcFZ5858QA2vvx1Ur5xIcixXIP+8LnFDgRplU30us6teqdlskFfu+ae4K79Ooew==",
      "license": "MIT",
      "dependencies": {
        "prelude-ls": "^1.2.1"
      },
      "engines": {
        "node": ">= 0.8.0"
      }
    }
  }
}

{
  "name": "sample-levn",
  "version": "1.0.0",
  "description": "Clean-room verification for levn.parse",
  "main": "src/index.js",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "levn": "0.4.1"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify levn.parse in pkg:npm/levn@0.4.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/levn@0.4.1"
  ],
  "symbols": [
    "levn.parse"
  ]
}

const levn = require('levn');

/**
 * Parses a string input into a JavaScript value based on the specified type.
 * @param {string} type - Type specification string.
 * @param {string} input - Levn formatted string input.
 * @param {object} [options] - Optional parsing options.
 * @returns {*} Parsed JavaScript value.
 */
function parseValue(type, input, options) {
  return levn.parse(type, input, options);
}

module.exports = {
  parseValue,
  levn,
};

import assert from 'node:assert';
import { createRequire } from 'node:module';

const require = createRequire(import.meta.url);
const { parseValue, levn } = require('../src/index.js');

async function runContract() {
  // 1. levn.parse parses primitive types including Number, String, Boolean, Undefined, Null, and NaN from string notation
  assert.strictEqual(parseValue('Number', '42'), 42);
  assert.strictEqual(parseValue('Number', '3.14'), 3.14);
  assert.strictEqual(parseValue('String', 'hello world'), 'hello world');
  assert.strictEqual(parseValue('Boolean', 'true'), true);
  assert.strictEqual(parseValue('Boolean', 'false'), false);
  assert.strictEqual(parseValue('Undefined', 'undefined'), undefined);
  assert.strictEqual(parseValue('Null', 'null'), null);
  assert.strictEqual(Number.isNaN(parseValue('NaN', 'NaN')), true);

  // 2. levn.parse parses composite types including arrays, tuples, and objects with nested type specifications
  assert.deepStrictEqual(parseValue('[Number]', '1, 2, 3'), [1, 2, 3]);
  assert.deepStrictEqual(parseValue('[String]', 'foo, bar, baz'), ['foo', 'bar', 'baz']);
  assert.deepStrictEqual(parseValue('(String, Number, Boolean)', 'alice, 30, true'), ['alice', 30, true]);
  assert.deepStrictEqual(
    parseValue('{name: String, count: Number}', 'name: item, count: 5'),
    { name: 'item', count: 5 }
  );

  // 3. levn.parse parses special types including Date literals and RegExp patterns with optional delimiters and flags
  const parsedDate = parseValue('Date', '2025-01-15');
  assert.ok(parsedDate instanceof Date);
  assert.strictEqual(parsedDate.getUTCFullYear(), 2025);

  const parsedRegExp = parseValue('RegExp', '/[a-z]+/i');
  assert.ok(parsedRegExp instanceof RegExp);
  assert.strictEqual(parsedRegExp.test('ABC'), true);

  const unquotedRegExp = parseValue('RegExp', 'hello');
  assert.ok(unquotedRegExp instanceof RegExp);
  assert.strictEqual(unquotedRegExp.test('hello'), true);

  // 4. levn.parse parses union types by attempting candidate type conversions in left-to-right precedence order
  assert.strictEqual(parseValue('Number | String', '123'), 123);
  assert.strictEqual(parseValue('Number | String', 'sample-text'), 'sample-text');
  assert.strictEqual(parseValue('Boolean | Number', 'true'), true);
  assert.strictEqual(parseValue('Boolean | Number', '99'), 99);

  // 5. levn.parse supports explicit mode using wildcard type or explicit option to require unambiguous literal syntax
  assert.deepStrictEqual(parseValue('*', '[1, "two", true]'), [1, 'two', true]);
  assert.strictEqual(parseValue('String', 'value', { explicit: true }), 'value');
  assert.throws(() => {
    parseValue('RegExp', 'not-a-regex-literal', { explicit: true });
  }, /does not type check/);

  // 6. levn.parse supports custom type definitions with custom typeOf, validate, and cast functions
  const customOptions = {
    customTypes: {
      EvenNumber: {
        typeOf: 'Number',
        validate: function(x) {
          return typeof x === 'number' && x % 2 === 0;
        },
        cast: function(val) {
          const num = parseInt(val, 10);
          return isNaN(num) ? { type: 'Nothing' } : { type: 'Just', value: num };
        }
      }
    }
  };
  assert.strictEqual(parseValue('EvenNumber', '8', customOptions), 8);
  assert.throws(() => {
    parseValue('EvenNumber', '9', customOptions);
  }, /does not type check/);

  // 7. levn.parse throws an error when the input string does not conform to the expected type
  assert.throws(() => {
    parseValue('Number', 'not-a-number');
  }, /does not type check/);

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

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