#  [](https://www.npmjs.com/package/@thi.ng/errors)  [](https://mastodon.thi.ng/@toxi) > [!NOTE] > This is one of 214 standalone projects, maintained as part > of the [@thi.ng/umbrella](https://github.com/thi-ng/umbrella/) monorepo > and anti-framework. > > 🚀 Please help me to work full-time on these projects by [sponsoring me on > GitHub](https://github.com/sponsors/postspectacular). 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://github.com/thi-ng/umbrella/tree/develop/packages/errors/src/assert.ts) - [`IllegalArgumentError`](https://github.com/thi-ng/umbrella/tree/develop/packages/errors/src/illegal-arguments.ts) - [`IllegalArityError`](https://github.com/thi-ng/umbrella/tree/develop/packages/errors/src/illegal-arity.ts) - [`IllegalStateError`](https://github.com/thi-ng/umbrella/tree/develop/packages/errors/src/illegal-statre.ts) - [`OutOfBoundsError`](https://github.com/thi-ng/umbrella/tree/develop/packages/errors/src/out-of-bounds.ts) - [`UnsupportedOperationError`](https://github.com/thi-ng/umbrella/tree/develop/packages/errors/src/unsupported.ts) Custom error types can be easily defined using [`defError()`](https://github.com/thi-ng/umbrella/tree/develop/packages/errors/src/deferror.ts). ## Status **STABLE** - used in production [Search or submit any issues for this package](https://github.com/thi-ng/umbrella/issues?q=%5Berrors%5D+in%3Atitle) ## 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://github.com/thi-ng/umbrella/tree/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://github.com/thi-ng/umbrella/tree/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