AssertExtends

Since 1.3.0

Assert that type T extends U at compile time.

Signature

type AssertExtends<T, U> = T extends U ? T : never

Parameters

Parameter	Description
T	The type to check
U	The type that T must extend

Examples

Basic Usage

import type { AssertExtends } from 'uni-types'

type Result = AssertExtends<'hello', string> // 'hello'
type Failed = AssertExtends<number, string> // never

With Union Types

type Result = AssertExtends<'a' | 'b', string> // 'a' | 'b'

With Object Types

type Extended = AssertExtends<{ name: string; age: number }, { name: string }> // { name: string; age: number }

Related

• AssertEqual - Assert types are equal
• AssertKeyof - Assert key exists on type