Type Assertions in typescript

typeAssertions.ts

// Type assertions, before I discovered https://www.npmjs.com/package/type-assertions

type AssertExtends<A, B> = A extends B ? true : false
export const assertExtends = <A, B>(_: AssertExtends<A, B>): void => {}
export const assertInstance = <B>(
  a: any,
  _: AssertExtends<typeof a, B>
): void => {}

assertExtends<'abc', string>(true)
assertExtends<string, 'abc'>(false)

interface Foo {
  foo: number
  bar: string
}

assertExtends<{ foo: number; bar: string }, Foo>(true)
assertExtends<{ foo: number; bar: string; baz: string }, Foo>(true)
assertExtends<{ foo: number; bar: number }, Foo>(false)
assertExtends<{ foo: number }, Foo>(false)

assertInstance<Foo>({ foo: 1, bar: 's' }, true)
assertInstance<Foo>({ foo: 1, bar: 's' }, true)