fix: types for waterfall hooks

lib/__tests__/AsyncSeriesHooks.js

@@ -71,6 +71,35 @@ describe("AsyncSeriesWaterfallHook", () => {
 
 		expect(result).toMatchSnapshot();
 	});
+
+	it("should work with undefined", async () => {
+		const hook = new AsyncSeriesWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => undefined);
+		return expect(hook.promise()).resolves.toBe(42);
+	});
+
+	it("should work with void", async () => {
+		const hook = new AsyncSeriesWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => {});
+		return expect(hook.promise()).resolves.toBe(42);
+	});
+
+	it("should work with undefined and number again", async () => {
+		const hook = new AsyncSeriesWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => {});
+		hook.tap("number-again", () => 43);
+		return expect(hook.promise()).resolves.toBe(43);
+	});
+
+	it("should work with null", async () => {
+		const hook = new AsyncSeriesWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => null);
+		return expect(hook.promise()).resolves.toBeNull();
+	});
 });
 
 describe("AsyncSeriesLoopHook", () => {

lib/__tests__/SyncWaterfallHook.js

@@ -22,6 +22,43 @@ describe("SyncWaterfallHook", () => {
 		);
 	});
 
+	it("should work", () => {
+		const hook = new SyncWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("string", () => "str");
+		hook.tap("false", () => false);
+		return expect(hook.call()).toBe(false);
+	});
+
+	it("should work with undefined", async () => {
+		const hook = new SyncWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => undefined);
+		return expect(hook.call()).toBe(42);
+	});
+
+	it("should work with void", async () => {
+		const hook = new SyncWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => {});
+		return expect(hook.call()).toBe(42);
+	});
+
+	it("should work with undefined and number again", async () => {
+		const hook = new SyncWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => {});
+		hook.tap("number-again", () => 43);
+		return expect(hook.call()).toBe(43);
+	});
+
+	it("should work with null", async () => {
+		const hook = new SyncWaterfallHook(["x"]);
+		hook.tap("number", () => 42);
+		hook.tap("undefined", () => null);
+		return expect(hook.call()).toBeNull();
+	});
+
 	it("should allow to create sync hooks", async () => {
 		const hook = new SyncWaterfallHook(["arg1", "arg2"]);
 

tapable.d.ts

@@ -95,7 +95,7 @@ export class SyncLoopHook<
 export class SyncWaterfallHook<
 	T,
 	AdditionalOptions = UnsetAdditionalOptions
-> extends SyncHook<T, AsArray<T>[0], AdditionalOptions> {}
+> extends SyncHook<T, AsArray<T>[0] | void, AdditionalOptions> {}
 
 declare class AsyncHook<
 	T,
@@ -137,7 +137,7 @@ export class AsyncSeriesLoopHook<
 export class AsyncSeriesWaterfallHook<
 	T,
 	AdditionalOptions = UnsetAdditionalOptions
-> extends AsyncHook<T, AsArray<T>[0], AdditionalOptions> {}
+> extends AsyncHook<T, AsArray<T>[0] | void, AdditionalOptions> {}
 
 type HookFactory<H> = (key: any, hook?: H) => H;