Add getKnownPropertyNames

src/misc.test-d.ts

@@ -1,6 +1,11 @@
 import { expectAssignable, expectNotAssignable, expectType } from 'tsd';
 
-import { isObject, hasProperty, RuntimeObject } from './misc';
+import {
+  isObject,
+  hasProperty,
+  getKnownPropertyNames,
+  RuntimeObject,
+} from './misc';
 
 //=============================================================================
 // isObject
@@ -99,6 +104,19 @@ if (hasProperty(hasPropertyTypeExample, 'a')) {
   expectType<number | undefined>(hasPropertyTypeExample.a);
 }
 
+//=============================================================================
+// getKnownPropertyNames
+//=============================================================================
+
+enum GetKnownPropertyNamesEnumExample {
+  Foo = 'bar',
+  Baz = 'qux',
+}
+
+expectType<('Foo' | 'Baz')[]>(
+  getKnownPropertyNames(GetKnownPropertyNamesEnumExample),
+);
+
 //=============================================================================
 // RuntimeObject
 //=============================================================================

src/misc.test.ts

@@ -3,6 +3,7 @@ import {
   isNullOrUndefined,
   isObject,
   hasProperty,
+  getKnownPropertyNames,
   RuntimeObject,
   isPlainObject,
   calculateNumberSize,
@@ -116,6 +117,21 @@ describe('miscellaneous', () => {
     });
   });
 
+  describe('getKnownPropertyNames', () => {
+    it('returns the own property names of the object', () => {
+      const object = { foo: 'bar', baz: 'qux' };
+
+      expect(getKnownPropertyNames(object)).toStrictEqual(['foo', 'baz']);
+    });
+
+    it('does not return inherited properties', () => {
+      const superObject = { foo: 'bar' };
+      const object = Object.create(superObject);
+
+      expect(getKnownPropertyNames(object)).toStrictEqual([]);
+    });
+  });
+
   describe('isPlainObject', () => {
     it('should return true for a plain object', () => {
       const somePlainObject = {

src/misc.ts

@@ -99,6 +99,23 @@ export const hasProperty = <
     Property extends keyof ObjectToCheck ? ObjectToCheck[Property] : unknown
   > => Object.hasOwnProperty.call(objectToCheck, name);
 
+/**
+ * `Object.getOwnPropertyNames()` is intentionally generic: it returns the
+ * immediate property names of an object, but it cannot make guarantees about
+ * the contents of that object, so the type of the property names is merely
+ * `string[]`. While this is technically accurate, it is also unnecessary if we
+ * have an object with a type that we own (such as an enum).
+ *
+ * @param object - The plain object.
+ * @returns The own property names of the object which are assigned a type
+ * derived from the object itself.
+ */
+export function getKnownPropertyNames<Key extends PropertyKey>(
+  object: Partial<Record<Key, any>>,
+): Key[] {
+  return Object.getOwnPropertyNames(object) as Key[];
+}
+
 export type PlainObject = Record<number | string | symbol, unknown>;
 
 /**