eslint-plugin-expect-type

ESLint plugin with ^? Twoslash, $ExpectError, and $ExpectType type assertions. 🧩

``ts
let value = 9001;
// ^? let value: number

// $ExpectError
value = "over nine thousand";

// $ExpectType number
9001;
`

Installation

Make sure you have TypeScript and @typescript-eslint/parser installed, then install the plugin:

`sh
npm i -D eslint-plugin-expect-type
`

> See typescript-eslint's Getting Started docs for how to run ESLint on TypeScript files.

Usage

Add the following options to your ESLint configuration file:

`ts
import expectType from "eslint-plugin-expect-type/configs/recommended";

export default [
// your other ESLint configurations
expectType,
];
`

> For CommonJS, use const expectType = require("eslint-plugin-expect-type/configs/recommended").default;.

Then, you'll be able to use ^?, $ExpectError, $ExpectType, and $ExpectTypeSnapshot comments in code assert on types.

$3

If you're still using the legacy ESLint configuration file format:

`json
{
"extends": ["plugin:expect-type/recommended"],
"plugins": ["expect-type"]
}
`

Rules

💼 Configurations enabled in.\
✅ Set in the recommended configuration.\
🔧 Automatically fixable by the --fix CLI option.\
💭 Requires type information.

| Name | Description | 💼 | 🔧 | 💭 |
| :----------------------------- | :------------------------------------------ | :- | :- | :- |
| expect | Expects type error, type snapshot, or type. | ✅ | 🔧 | 💭 |

References

You might consider using other popular libraries and tools that can run type assertions:

- expect-type: Provides functions that return assorted generic type assertion methods, such as expectTypeOf('abc').toMatchTypeOf().
- ts-expect: Provides generic type assertion function, used like expectType('abc')().
- tsd: Allows writing tests specifically for .d.ts definition files.
- TSTyche: A type testing tool that ships with describe() and test() helpers, expect style assertions and a mighty test runner which allows to use specified version of TypeScript.
- Vitest: Includes assertType and expectTypeOf assertions.

TypeScript Version Support

eslint-plugin-expect-type` mirrors the DefinitelyTyped TypeScript Support Window.
Roughly, that's major versions of TypeScript less than 2 years old.

Appreciation

Many thanks to @ibezkrovnyi for creating the initial version and core infrastructure of this package! 💖

Contributors

Batuhan Wilhelm 🐛 💻	Colin 🐛	Cédric Exbrayat 🐛	Dan Vanderkam 💻 🚧	Daniel Nagy 🐛	Dominik Dorfmeister 📖	Francesco Trotta 💻 🐛
Igor Bezkrovnyi 🐛 💻 📖 🚧	Josh Goldberg ✨ 🐛 💻 📖 🚧 🚇 🤔 🔧	Russell Davis 💻	Tom Mrazauskas 📖	detachhead 🤔	nirtamir2 📖

> 💙 This package was templated with create-typescript-app.