fix: record type absorbed into empty object type

fixes #13

Author: uhyo

generated/lib.es2022.object.d.ts

@@ -4,20 +4,21 @@ interface ObjectConstructor {
    * @param o An object.
    * @param v A property name.
    */
-  hasOwn<Key extends PropertyKey>(
-    o: object,
+  hasOwn<Obj extends object, Key extends PropertyKey>(
+    o: Obj,
     v: Key
-  ): o is string extends Key
-    ? {}
-    : number extends Key
-    ? {}
-    : symbol extends Key
-    ? {}
-    : Key extends PropertyKey
-    ? {
-        [key in Key]: unknown;
-      }
-    : {};
+  ): o is Obj &
+    (string extends Key
+      ? {}
+      : number extends Key
+      ? {}
+      : symbol extends Key
+      ? {}
+      : Key extends PropertyKey
+      ? {
+          [key in Key]: unknown;
+        }
+      : {});
 }
 //     /**
 //      * Determines whether an object has a property with the specified name.

generated/lib.es5.d.ts

@@ -122,19 +122,21 @@ interface Object {
    * Determines whether an object has a property with the specified name.
    * @param v A property name.
    */
-  hasOwnProperty<Key extends PropertyKey>(
+  hasOwnProperty<Obj, Key extends PropertyKey>(
+    this: Obj,
     v: Key
-  ): this is string extends Key
-    ? {}
-    : number extends Key
-    ? {}
-    : symbol extends Key
-    ? {}
-    : Key extends PropertyKey
-    ? {
-        [key in Key]: unknown;
-      }
-    : {};
+  ): this is Obj &
+    (string extends Key
+      ? {}
+      : number extends Key
+      ? {}
+      : symbol extends Key
+      ? {}
+      : Key extends PropertyKey
+      ? {
+          [key in Key]: unknown;
+        }
+      : {});
 
   /**
    * Determines whether an object exists in another object's prototype chain.

lib/lib.es2022.object.d.ts

@@ -4,16 +4,17 @@ interface ObjectConstructor {
    * @param o An object.
    * @param v A property name.
    */
-  hasOwn<Key extends PropertyKey>(
-    o: object,
+  hasOwn<Obj extends object, Key extends PropertyKey>(
+    o: Obj,
     v: Key
-  ): o is string extends Key
-    ? {}
-    : number extends Key
-    ? {}
-    : symbol extends Key
-    ? {}
-    : Key extends PropertyKey
-    ? { [key in Key]: unknown }
-    : {};
+  ): o is Obj &
+    (string extends Key
+      ? {}
+      : number extends Key
+      ? {}
+      : symbol extends Key
+      ? {}
+      : Key extends PropertyKey
+      ? { [key in Key]: unknown }
+      : {});
 }

lib/lib.es5.d.ts

@@ -26,17 +26,18 @@ interface Object {
    * Determines whether an object has a property with the specified name.
    * @param v A property name.
    */
-  hasOwnProperty<Key extends PropertyKey>(
+  hasOwnProperty<Obj, Key extends PropertyKey>(
+    this: Obj,
     v: Key
-  ): this is string extends Key
+  ): this is Obj & (string extends Key
     ? {}
     : number extends Key
     ? {}
     : symbol extends Key
     ? {}
     : Key extends PropertyKey
     ? { [key in Key]: unknown }
-    : {};
+    : {});
 }
 
 interface ObjectConstructor {

tests/src/es2022.object.ts

@@ -6,7 +6,7 @@ import { expectError, expectType } from "tsd";
   const obj: object = {};
   if (Object.hasOwn(obj, "foo")) {
     expectType<unknown>(obj.foo);
-    expectType<{ foo: unknown }>(obj);
+    expectType<object & { foo: unknown }>(obj);
   }
   const obj2 = { foo: 123 };
   if (Object.hasOwn(obj2, "bar")) {
@@ -31,3 +31,17 @@ import { expectError, expectType } from "tsd";
     expectType<{}>(emptyObj);
   }
 }
+
+// https://github.com/uhyo/better-typescript-lib/issues/13
+{
+  const protoObj = { protoProp: 'protoProp' };
+
+  const obj: Record<string, string> = Object.create(protoObj);
+  obj.ownProp = 'ownProp';
+
+  for (const key in obj) {
+    if (!Object.hasOwn(obj, key)) continue;
+    expectType<Record<string, string>>(obj);
+    obj[key];
+  }
+}

tests/src/es5.ts

@@ -43,7 +43,7 @@ expectType<{ foo: number; bar: string; baz: boolean }>(
   const obj: object = {};
   if (obj.hasOwnProperty("foo")) {
     expectType<unknown>(obj.foo);
-    expectType<{ foo: unknown }>(obj);
+    expectType<object & { foo: unknown }>(obj);
   }
   const obj2 = { foo: 123 };
   if (obj2.hasOwnProperty("bar")) {
@@ -69,6 +69,20 @@ expectType<{ foo: number; bar: string; baz: boolean }>(
   }
 }
 
+// https://github.com/uhyo/better-typescript-lib/issues/13
+{
+  const protoObj = { protoProp: 'protoProp' };
+
+  const obj: Record<string, string> = Object.create(protoObj);
+  obj.ownProp = 'ownProp';
+
+  for (const key in obj) {
+    if (!obj.hasOwnProperty(key)) continue;
+    expectType<Record<string, string>>(obj);
+    obj[key];
+  }
+}
+
 // ObjectConstructor
 {
   // Object.defineProperty
@@ -309,4 +323,5 @@ expectType<{ foo: number; bar: string; baz: boolean }>(
   }
 }
 
-export {};
+export { };
+