# @thi.ng/errors > Custom error types and error factory functions Latest version **2.6.17** (published 2026-08-25) · Apache-2.0 license · 0 weekly downloads ## Install ```sh npm install @thi.ng/errors pnpm add @thi.ng/errors yarn add @thi.ng/errors bun add @thi.ng/errors ``` ## Health **Score 70/100 (B)** — status: active. Positive: has types; esm support; no vulnerabilities; recently updated; high maintenance score; high quality score. Warnings: low downloads. ## Facts | | | |---|---| | Version | 2.6.17 | | Published | 2026-08-25 | | First published | 2018-05-10 | | Weekly downloads | 0 | | License | Apache-2.0 | | TypeScript types | bundled | | Module format | ESM | | Node | >=18 | | Dependencies | 0 | | Unpacked size | 32.1 KB | | Known vulnerabilities | 0 | | Install scripts | no | | Author | Karsten Schmidt | | Maintainers | thi.ng | | Keywords | assert, errors, typescript | ## Links - npm: https://www.npmjs.com/package/@thi.ng/errors - Repository: https://codeberg.org/thi.ng/umbrella - Homepage: https://thi.ng/errors - Funding: https://github.com/sponsors/postspectacular - npm.io page: https://npm.io/package/@thi.ng/errors ## Alternatives - [@openai/codex-sdk](https://npm.io/package/@openai/codex-sdk.md) — 731.4K weekly downloads - [babel-plugin-transform-react-jsx](https://npm.io/package/babel-plugin-transform-react-jsx.md) — 565.0K weekly downloads - [babel-helper-remove-or-void](https://npm.io/package/babel-helper-remove-or-void.md) — 508.5K weekly downloads - [@pnpm/store-controller-types](https://npm.io/package/@pnpm/store-controller-types.md) — 186.9K weekly downloads - [react-native-signature-canvas](https://npm.io/package/react-native-signature-canvas.md) — 155.6K weekly downloads ## Recent versions - 2.6.17 (latest) — 2026-08-25 - 2.6.16 — 2026-07-02 - 2.6.15 — 2026-06-05 - 2.6.14 — 2026-05-23 - 2.6.13 — 2026-05-20 - 2.6.11 — 2026-05-11 - 2.6.10 — 2026-05-08 - 2.6.9 — 2026-04-26 - 2.6.8 — 2026-04-18 - 2.6.7 — 2026-04-02 - 2.6.6 — 2026-03-19 - 2.6.5 — 2026-03-07 - 2.6.4 — 2026-03-07 - 2.6.3 — 2026-02-07 - 2.6.2 — 2026-01-23 - … 176 more at https://npm.io/package/@thi.ng/errors/versions ## README # ![@thi.ng/errors](https://codeberg.org/thi.ng/umbrella/media/branch/develop/assets/banners/thing-errors.svg?d7513125) [![npm version](https://img.shields.io/npm/v/@thi.ng/errors.svg)](https://www.npmjs.com/package/@thi.ng/errors) ![npm downloads](https://img.shields.io/npm/dm/@thi.ng/errors.svg) [![Mastodon Follow](https://img.shields.io/mastodon/follow/109331703950160316?domain=https%3A%2F%2Fmastodon.thi.ng&style=social)](https://mastodon.thi.ng/@toxi) > [!NOTE] > This is one of 217 standalone projects. LLM-free, human-made and > cared for software, maintained as part of the > [@thi.ng/umbrella](https://codeberg.org/thi.ng/umbrella/) ecosystem and > anti-framework. > > 🚀 Please help me to work full-time on these projects by [sponsoring > me](https://codeberg.org/thi.ng/umbrella/src/branch/develop/CONTRIBUTING.md#donations). > Thank you! ❤️ - [About](#about) - [Status](#status) - [Installation](#installation) - [Dependencies](#dependencies) - [Usage examples](#usage-examples) - [API](#api) - [Environment variables](#environment-variables) - [Authors](#authors) - [License](#license) ## About Custom error types and error factory functions. This package defines the following error types & helper functions to throw them: - [`AssertionError`](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors/src/assert.ts) - [`IllegalArgumentError`](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors/src/illegal-arguments.ts) - [`IllegalArityError`](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors/src/illegal-arity.ts) - [`IllegalStateError`](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors/src/illegal-statre.ts) - [`OutOfBoundsError`](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors/src/out-of-bounds.ts) - [`UnsupportedOperationError`](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors/src/unsupported.ts) Custom error types can be easily defined using [`defError()`](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors/src/deferror.ts). ## Status **STABLE** - used in production [Search or submit any issues for this package](https://codeberg.org/thi.ng/umbrella/issues?q=%5Berrors%5D) ## Installation ```bash yarn add @thi.ng/errors ``` ESM import: ```ts import * as err from "@thi.ng/errors"; ``` Browser ESM import: ```html ``` [JSDelivr documentation](https://www.jsdelivr.com/) For Node.js REPL: ```js const err = await import("@thi.ng/errors"); ``` Package sizes (brotli'd, pre-treeshake): ESM: 849 bytes ## Dependencies None ## Usage examples One project in this repo's [/examples](https://codeberg.org/thi.ng/umbrella/src/branch/develop/examples) directory is using this package: | Description | Live demo | Source | |:-----------------------------------------------------------------------------|:---------------------------------------------------|:----------------------------------------------------------------------------------------| | GPU-based data reduction using thi.ng/shader-ast & WebGL multi-pass pipeline | [Demo](https://demo.thi.ng/umbrella/gpgpu-reduce/) | [Source](https://codeberg.org/thi.ng/umbrella/src/branch/develop/examples/gpgpu-reduce) | ## API [Generated API docs](https://docs.thi.ng/umbrella/errors/) ```ts import * as err from "@thi.ng/errors"; err.illegalArity(3) // Error: illegal arity: 3 err.illegalArgs("expected foo"); // Error: illegal argument(s): expected foo err.illegalState("oops"); // Error: illegal state: oops err.unsupported("TODO not yet implemented") // Error: unsupported operation: TODO not yet implemented // define custom error const MyError = err.defError( () => "Eeek... ", (x) => x + " is not allowed!" ); try { throw new MyError(23); } catch(e) { console.warn(e.message); console.log(e instanceof Error); } // Eeek... 23 is not allowed! // true ``` ### Environment variables The `UMBRELLA_ASSERTS` or `VITE_UMBRELLA_ASSERTS` env variables are used to control the behavior of the `assert()` function in production builds: If either is set (to a non-empty string), the function will **always** be enabled. Otherwise (by default), `assert()` will be **disabled for production builds**, i.e. if `process.env.NODE_ENV === "production"`. ## Authors - [Karsten Schmidt](https://thi.ng) If this project contributes to an academic publication, please cite it as: ```bibtex @misc{thing-errors, title = "@thi.ng/errors", author = "Karsten Schmidt", note = "https://thi.ng/errors", year = 2018 } ``` ## License © 2018 - 2026 Karsten Schmidt // Apache License 2.0 --- _Source: https://npm.io/package/@thi.ng/errors · Machine-readable twin of the npm.io package page. 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