Class: Fix type inference (#701)

sindresorhus · Nov 13, 2023 · 7294cf0 · 7294cf0
1 parent 59411c8
commit 7294cf0
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Showing 3 changed files with 59 additions and 4 deletions.
diff --git a/source/basic.d.ts b/source/basic.d.ts
@@ -4,7 +4,7 @@ Matches a [`class`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe
 @category Class
 */
 export type Class<T, Arguments extends unknown[] = any[]> = {
-	prototype: T;
+	prototype: Pick<T, keyof T>;
 	new(...arguments_: Arguments): T;
 };
 
@@ -25,7 +25,7 @@ We cannot use a `type` here because TypeScript throws: 'abstract' modifier canno
 */
 // eslint-disable-next-line @typescript-eslint/consistent-type-definitions
 export interface AbstractClass<T, Arguments extends unknown[] = any[]> extends AbstractConstructor<T, Arguments> {
-	prototype: T;
+	prototype: Pick<T, keyof T>;
 }
 
 /**

diff --git a/test-d/abstract-class.ts b/test-d/abstract-class.ts
@@ -1,5 +1,5 @@
-import {expectError, expectAssignable, expectNotAssignable} from 'tsd';
-import type {AbstractConstructor, AbstractClass} from '../index';
+import {expectError, expectAssignable, expectNotAssignable, expectType} from 'tsd';
+import type {AbstractConstructor, AbstractClass, IsAny} from '../index';
 
 abstract class Foo {
 	constructor(x: number) {
@@ -59,3 +59,31 @@ expectNotAssignable<{fooMethod(): void}>(Bar.prototype);
 expectError(new CorrectConcreteExtendedBar(12));
 expectAssignable<{barMethod(): void}>(new CorrectConcreteExtendedBar(12, 15));
 // /Prototype test
+
+// Prototype test with type parameter
+abstract class AbstractBuilding<T = unknown> {
+	owners: T;
+	constructor(buildingOwners: T) {
+		this.owners = buildingOwners;
+	}
+}
+
+type Census = {
+	count: number;
+};
+
+abstract class House<OwnerCount extends Census = Census> extends AbstractBuilding<OwnerCount> {}
+
+class CityBlock<BuildingType extends AbstractBuilding<Census>> {
+	residence: BuildingType;
+
+	constructor(HousingType: AbstractClass<BuildingType, [Census]>) {
+		class Building extends HousingType {}
+		this.residence = new Building({count: 2});
+	}
+}
+
+const Family = (new CityBlock(House)).residence.owners;
+expectType<IsAny<typeof Family>>(false);
+expectAssignable<number>(Family.count);
+// /Prototype test with type parameter
diff --git a/test-d/class.ts b/test-d/class.ts
@@ -54,3 +54,30 @@ expectType<PositionProps>(Position.prototype);
 
 expectError(new Position(17));
 expectAssignable<PositionProps>(new Position(17, 34));
+
+// Prototype test with type parameter
+class Building<T = unknown> {
+	owners: T;
+	constructor(buildingOwners: T) {
+		this.owners = buildingOwners;
+	}
+}
+
+type Census = {
+	count: number;
+};
+
+class House<OwnerCount extends Census = Census> extends Building<OwnerCount> {}
+
+class CityBlock<BuildingType extends Building> {
+	residence: BuildingType;
+
+	constructor(HousingType: Class<BuildingType, [Census]>) {
+		this.residence = new HousingType({count: 2});
+	}
+}
+
+const Family = (new CityBlock(House)).residence.owners;
+expectType<IsAny<typeof Family>>(false);
+expectAssignable<number>(Family.count);
+// /Prototype test with type parameter