https://github.com/dsherret/conditional-type-checks

Types for testing TypeScript types.
https://github.com/dsherret/conditional-type-checks

Last synced: 19 days ago
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Types for testing TypeScript types.

• Host: GitHub
• URL: https://github.com/dsherret/conditional-type-checks
• Owner: dsherret
• License: mit
• Created: 2018-04-05T00:42:10.000Z (over 6 years ago)
• Default Branch: main
• Last Pushed: 2022-06-18T19:21:01.000Z (over 2 years ago)
• Last Synced: 2024-10-04T10:11:06.663Z (about 1 month ago)
• Language: TypeScript
• Size: 50.8 KB
• Stars: 450
• Watchers: 10
• Forks: 19
• Open Issues: 8
• Metadata Files:
  • Readme: README.md
  • License: LICENSE
  • Code of conduct: .github/CODE_OF_CONDUCT.md

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README

        
# Conditional Type Checks

[![npm version](https://badge.fury.io/js/conditional-type-checks.svg)](https://badge.fury.io/js/conditional-type-checks)

[![CI](https://github.com/dsherret/conditional-type-checks/workflows/CI/badge.svg)](https://github.com/dsherret/conditional-type-checks/actions?query=workflow%3ACI)

[![deno doc](https://doc.deno.land/badge.svg)](https://doc.deno.land/https/deno.land/x/conditional_type_checks/mod.ts)

[![stable](http://badges.github.io/stability-badges/dist/stable.svg)](http://github.com/badges/stability-badges)

As TypeScript's type system becomes more complex, it's useful to be able to write tests for what a type should be.

This library offers reusable conditional types to help test your types.

## Type Checks

These will resolve to the type `true` when they match and `false` otherwise.

- `IsNullable` - Checks if `T` is possibly `null` or `undefined`.

- `IsExact` - Checks if `T` exactly matches `U`.

- `Has` - Checks if `T` has `U`.

- `NotHas` - Checks if `T` does not have `U`.

- `IsAny` - Checks if `T` is the `any` type.

- `IsNever` - Checks if `T` is the `never` type.

- `IsUnknown` - Checks if `T` is the `unknown` type.

- More to come...

## Ways to Test

Use what you prefer:

1. The `AssertTrue`, `AssertFalse`, or `Assert` types.

2. The `assert` function.

### Use with `AssertTrue`, `AssertFalse`, and `Assert`

Doing a test:

```ts

import type {

  AssertFalse,

  AssertTrue,

  Has,

  IsNever,

  IsNullable,

} from "https://deno.land/x/conditional_type_checks/mod.ts";

const result = someFunction(someArg);

type _test =

  | AssertTrue | IsNullable>

  | AssertFalse>

  | Assert, true>;

```

**Warning:** Do not use an intersection type between checks (ex. `Has & IsNever`) because it will cause everything to pass if only one of the checks passes.

### Use with `assert`

Doing a test:

```ts

import {

  assert,

  IsExact,

} from "https://deno.land/x/conditional_type_checks/mod.ts";

const result = someFunction(someArg);

// compile error if the type of `result` is not exactly `string | number`

assert>(true);

```

Failure:

```ts

// causes a compile error that `true` is not assignable to `false`

assert>(true); // string is not nullable

```

## npm Install

```

npm install --save-dev conditional-type-checks

```