feat(typescript-types): Add OptionalKeysOf<T>

packages/typescript-types/test/optional-keys-of.tst.ts

@@ -0,0 +1,39 @@
+import type { OptionalKeysOf } from '@/optional-keys-of.js'
+import { expect } from 'tstyche'
+
+interface Example1 {
+	requiredKey: number
+	optionalKey?: number
+	anotherOptional?: string
+	unknownNonOptionalKey: unknown
+	undefinedNonOptionalKey: undefined
+	neverKey: never
+}
+
+interface Example2 {
+	requiredKey2: number
+	optionalKey2?: number
+	anotherOptional2?: string
+	unknownNonOptionalKey2: unknown
+	undefinedNonOptionalKey2: undefined
+	neverKey2: never
+}
+
+type ExpectKeyOf<T, K extends keyof T> = { [P in K]: T[P] }
+type KeysOfInGenericsPart<
+	Shape extends object,
+	Defaults extends Pick<Shape, OptionalKeysOf<Shape>>
+> = Defaults
+
+expect<OptionalKeysOf<Example1>>().type.toBe<'optionalKey' | 'anotherOptional'>()
+expect<OptionalKeysOf<Example2>>().type.toBe<'optionalKey2' | 'anotherOptional2'>()
+expect<OptionalKeysOf<Example1 | Example2>>().type.toBe<
+	'optionalKey' | 'anotherOptional' | 'optionalKey2' | 'anotherOptional2'
+>()
+
+expect<Pick<Example1, OptionalKeysOf<Example1>>>().type.toBe<
+	ExpectKeyOf<Example1, OptionalKeysOf<Example1>>
+>()
+
+type DefaultValues = { optionalKey: 1; anotherOptional2: 'asdf' }
+expect<KeysOfInGenericsPart<Example1, DefaultValues>>().type.toBe<DefaultValues>()