es-toolkit 1.50.0: isError

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 es-toolkit.isError in pkg:npm/es-toolkit@1.50.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/es-toolkit@1.50.0
Demonstrate these symbols/APIs:
  - es-toolkit.isError

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:aed093d291f911a3a1ace920dc0404d57f60b2e8c6eacccbad016602fdb4c0ea","contract":["isError is exported from es-toolkit root and es-toolkit/predicate subpath as the identical function","isError returns true for standard Error instances including TypeError and RangeError","isError returns true for custom error classes extending Error","isError returns false for non-error values including strings, numbers, booleans, and null or undefined","isError returns false for plain objects with error-like properties"],"goal":"verify es-toolkit.isError in pkg:npm/es-toolkit@1.50.0","kind":"HOW","packages":["pkg:npm/es-toolkit@1.50.0"],"schemaVersion":1,"symbols":["es-toolkit.isError"]},"contractCommand":["node","test/contract.js"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/es-toolkit@1.50.0"],"schemaVersion":1,"subject":"pkg:npm/es-toolkit@1.50.0","symbols":["es-toolkit.isError"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-es-toolkit-is-error",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-es-toolkit-is-error",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "es-toolkit": "1.50.0"
      }
    },
    "node_modules/es-toolkit": {
      "version": "1.50.0",
      "resolved": "https://registry.npmjs.org/es-toolkit/-/es-toolkit-1.50.0.tgz",
      "integrity": "sha512-OyZKhUVvEep9ITEiwHn8GKnMRQIVqoSIX7WnRbkWgJkllCujilqP2rD0u979tkl8wqyc8ICwlc1UBVv/Sl1G6w==",
      "license": "MIT",
      "workspaces": [
        "docs",
        "benchmarks",
        "tests/types"
      ]
    }
  }
}

{
  "name": "sample-es-toolkit-is-error",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "description": "Clean-room verification for es-toolkit isError",
  "main": "src/index.js",
  "scripts": {
    "test": "node test/contract.js"
  },
  "dependencies": {
    "es-toolkit": "1.50.0"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify es-toolkit.isError in pkg:npm/es-toolkit@1.50.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/es-toolkit@1.50.0"
  ],
  "symbols": [
    "es-toolkit.isError"
  ]
}

import { isError } from 'es-toolkit';
import { isError as isErrorFromSubpath } from 'es-toolkit/predicate';

/**
 * Validates whether a given value is an Error instance.
 * @param {unknown} value
 * @returns {boolean}
 */
export function checkIsError(value) {
  return isError(value);
}

/**
 * Checks if a value is an Error instance using the subpath export.
 * @param {unknown} value
 * @returns {boolean}
 */
export function checkIsErrorFromSubpath(value) {
  return isErrorFromSubpath(value);
}

export { isError, isErrorFromSubpath };

import assert from 'node:assert/strict';
import {
  isError,
  isErrorFromSubpath,
  checkIsError,
  checkIsErrorFromSubpath,
} from '../src/index.js';

// 1. isError is exported from es-toolkit root and es-toolkit/predicate subpath as the identical function
assert.equal(typeof isError, 'function', 'isError must be a function');
assert.equal(typeof isErrorFromSubpath, 'function', 'isError from subpath must be a function');
assert.equal(isError, isErrorFromSubpath, 'Root and subpath exports must be identical');

// 2. isError returns true for standard Error instances including TypeError and RangeError
assert.equal(checkIsError(new Error('test error')), true, 'standard Error must return true');
assert.equal(checkIsError(new TypeError('type error')), true, 'TypeError must return true');
assert.equal(checkIsError(new RangeError('range error')), true, 'RangeError must return true');
assert.equal(checkIsError(new SyntaxError('syntax error')), true, 'SyntaxError must return true');
assert.equal(checkIsError(new URIError('uri error')), true, 'URIError must return true');
assert.equal(checkIsError(new EvalError('eval error')), true, 'EvalError must return true');
assert.equal(checkIsError(new ReferenceError('ref error')), true, 'ReferenceError must return true');

// 3. isError returns true for custom error classes extending Error
class CustomAppError extends Error {
  constructor(msg) {
    super(msg);
    this.name = 'CustomAppError';
  }
}
assert.equal(checkIsError(new CustomAppError('custom failure')), true, 'Custom error class instance must return true');
assert.equal(checkIsErrorFromSubpath(new CustomAppError('custom failure')), true, 'Subpath check must return true for custom error');

// 4. isError returns false for non-error values including strings, numbers, booleans, and null or undefined
assert.equal(checkIsError('Error: something went wrong'), false, 'String must return false');
assert.equal(checkIsError(500), false, 'Number must return false');
assert.equal(checkIsError(true), false, 'Boolean must return false');
assert.equal(checkIsError(false), false, 'Boolean false must return false');
assert.equal(checkIsError(null), false, 'Null must return false');
assert.equal(checkIsError(undefined), false, 'Undefined must return false');
assert.equal(checkIsError(Symbol('error')), false, 'Symbol must return false');
assert.equal(checkIsError([new Error('nested')]), false, 'Array of errors must return false');

// 5. isError returns false for plain objects with error-like properties
assert.equal(checkIsError({ name: 'Error', message: 'fake error' }), false, 'Plain object with name and message must return false');
assert.equal(checkIsError({ stack: 'Error: fake\n at file.js:1:1' }), false, 'Plain object with stack must return false');

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