jest-util 30.4.1: deepCyclicCopy

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 jest-util.deepCyclicCopy in pkg:npm/jest-util@30.4.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/jest-util@30.4.1
Demonstrate these symbols/APIs:
  - jest-util.deepCyclicCopy

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.

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import { deepCyclicCopy } from 'jest-util';

export { deepCyclicCopy };

/**
 * Creates a deep clone of any value, preserving circular references and options.
 * @param {unknown} value
 * @param {{ blacklist?: Set<string>, keepPrototype?: boolean }} [options]
 * @returns {unknown}
 */
export function cloneDeep(value, options) {
  return deepCyclicCopy(value, options);
}

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{
  "name": "sample-jest-util-deep-cyclic-copy",
  "version": "1.0.0",
  "description": "Clean-room verification of jest-util.deepCyclicCopy",
  "type": "module",
  "main": "index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "jest-util": "30.4.1"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify jest-util.deepCyclicCopy in pkg:npm/jest-util@30.4.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/jest-util@30.4.1"
  ],
  "symbols": [
    "jest-util.deepCyclicCopy"
  ]
}

import assert from 'node:assert';
import { deepCyclicCopy, cloneDeep } from '../index.mjs';

// 1. deepCyclicCopy creates a deep copy of nested objects and arrays without mutating original structures
{
  const original = {
    title: 'root',
    count: 10,
    nested: {
      tags: ['alpha', 'beta', { key: 'value' }],
      flag: true
    }
  };
  const copy = deepCyclicCopy(original);
  assert.deepStrictEqual(copy, original);
  assert.notStrictEqual(copy, original);
  assert.notStrictEqual(copy.nested, original.nested);
  assert.notStrictEqual(copy.nested.tags, original.nested.tags);
  assert.notStrictEqual(copy.nested.tags[2], original.nested.tags[2]);

  copy.nested.tags[0] = 'modified';
  assert.strictEqual(original.nested.tags[0], 'alpha', 'mutating copy must not affect original');

  // Verify cloneDeep helper export
  const helperCopy = cloneDeep(original);
  assert.deepStrictEqual(helperCopy, original);
  assert.notStrictEqual(helperCopy, original);
}

// 2. deepCyclicCopy preserves circular references and shared object identities without infinite recursion
{
  const node = { id: 1 };
  node.self = node;
  const child = { parent: node };
  node.child = child;
  child.root = node;

  const copy = deepCyclicCopy(node);
  assert.notStrictEqual(copy, node);
  assert.strictEqual(copy.self, copy, 'self reference must point to copied node');
  assert.strictEqual(copy.child.parent, copy, 'child.parent must point to copied node');
  assert.strictEqual(copy.child.root, copy, 'child.root must point to copied node');
}

// 3. deepCyclicCopy preserves custom class prototype when keepPrototype option is true and strips prototype when false
{
  class Item {
    constructor(name) {
      this.name = name;
    }
    getName() {
      return this.name;
    }
  }

  const originalItem = new Item('widget');

  const plainCopy = deepCyclicCopy(originalItem, { keepPrototype: false });
  assert.strictEqual(plainCopy.name, 'widget');
  assert.strictEqual(Object.getPrototypeOf(plainCopy), Object.prototype);
  assert.strictEqual(typeof plainCopy.getName, 'undefined');

  const protoCopy = deepCyclicCopy(originalItem, { keepPrototype: true });
  assert.strictEqual(protoCopy.name, 'widget');
  assert.strictEqual(Object.getPrototypeOf(protoCopy), Item.prototype);
  assert.strictEqual(protoCopy.getName(), 'widget');
  assert.ok(protoCopy instanceof Item);
}

// 4. deepCyclicCopy excludes specified top-level property keys when blacklist option Set is provided
{
  const payload = {
    publicId: 'pub-42',
    secretKey: 'top-secret',
    internalMeta: 99,
    sub: {
      secretKey: 'nested-retained'
    }
  };
  const blacklist = new Set(['secretKey', 'internalMeta']);
  const copy = deepCyclicCopy(payload, { blacklist });

  assert.strictEqual(copy.publicId, 'pub-42');
  assert.strictEqual('secretKey' in copy, false);
  assert.strictEqual('internalMeta' in copy, false);
  assert.strictEqual(copy.sub.secretKey, 'nested-retained', 'blacklist only applies to top-level object');
}

// 5. deepCyclicCopy passes through primitives, null, and Buffer instances without modification
{
  assert.strictEqual(deepCyclicCopy(null), null);
  assert.strictEqual(deepCyclicCopy(undefined), undefined);
  assert.strictEqual(deepCyclicCopy(42), 42);
  assert.strictEqual(deepCyclicCopy('sample string'), 'sample string');
  assert.strictEqual(deepCyclicCopy(false), false);
  const sym = Symbol('token');
  assert.strictEqual(deepCyclicCopy(sym), sym);
  const buf = Buffer.from('payload bytes');
  const bufCopy = deepCyclicCopy(buf);
  assert.strictEqual(bufCopy, buf, 'Buffer instances must be returned by reference without modification');
}

// 6. deepCyclicCopy preserves accessor property descriptors including custom getters and setters
{
  let state = 5;
  const target = {
    get double() {
      return state * 2;
    }
  };
  const copy = deepCyclicCopy(target);
  const descriptor = Object.getOwnPropertyDescriptor(copy, 'double');
  assert.ok(descriptor !== undefined);
  assert.strictEqual(typeof descriptor.get, 'function');
  assert.strictEqual(descriptor.value, undefined);
  assert.strictEqual(copy.double, 10);
  state = 7;
  assert.strictEqual(copy.double, 14);
}

console.log('All contract assertions passed.');