feat(typescript-types): Add isKeyOf<T,K>

packages/typescript-types/test/is-key-of.tst.ts

@@ -0,0 +1,32 @@
+import type { IsKeyOf } from '@/is-key-of.js'
+import { expect } from 'tstyche'
+
+interface Example1 {
+	requiredKey: number
+	optionalKey?: number
+	unknownNonOptionalKey: unknown
+	undefinedNonOptionalKey: undefined
+	neverKey: never
+}
+
+expect<IsKeyOf<Example1, 'requiredKey'>>().type.toBe<true>()
+expect<IsKeyOf<Example1, 'optionalKey'>>().type.toBe<true>()
+expect<IsKeyOf<Example1, 'unknownNonOptionalKey'>>().type.toBe<true>()
+expect<IsKeyOf<Example1, 'undefinedNonOptionalKey'>>().type.toBe<true>()
+expect<IsKeyOf<Example1, 'neverKey'>>().type.toBe<true>()
+expect<IsKeyOf<string, 'toString'>>().type.toBe<true>()
+
+expect<IsKeyOf<any, 123>>().type.toBe<true>()
+expect<IsKeyOf<any, 'asdf'>>().type.toBe<true>()
+
+expect<IsKeyOf<Example1, 'unknown'>>().type.toBe<false>()
+expect<IsKeyOf<object, 'toString'>>().type.toBe<false>()
+
+expect<IsKeyOf<Example1, never>>().type.toBe<false>()
+expect<IsKeyOf<never, 'toString'>>().type.toBe<false>()
+expect<IsKeyOf<never, 'anystring'>>().type.toBe<false>()
+expect<IsKeyOf<never, 123>>().type.toBe<false>()
+expect<IsKeyOf<any, never>>().type.toBe<false>()
+expect<IsKeyOf<undefined, 123>>().type.toBe<false>()
+
+expect<IsKeyOf<Example1, any>>().type.toBe<boolean>()