feat: optionally return subscription dispose function directly from subscription function (#46)

Author: atheck

README.md

@@ -415,11 +415,11 @@ Then we write our `subscription` function:
 
 ```ts
 function subscription (model: Model): SubscriptionResult<Message> {
-    const sub = (dispatch: Dispatch<Message>): void => {
-        setInterval(() => dispatch(Msg.timer(new Date())), 1000) as unknown as number;
+    const sub = (dispatch: Dispatch<Message>) => {
+        setInterval(() => dispatch(Msg.timer(new Date())), 1000);
     }
 
-    return [cmd.ofSub(sub)];
+    return [sub];
 }
 ```
 
@@ -431,31 +431,29 @@ In the function component we call `useElmish` and pass the subscription to it:
 const [{ date }] = useElmish({ name: "Subscriptions", props, init, update, subscription })
 ```
 
-You can define and aggregate multiple subscriptions with a call to `cmd.batch(...)`.
+Because the return type is an array, you can define and return multiple subscription functions.
 
 ### Cleanup subscriptions
 
-In the solution above `setInterval` will trigger events even if the component is removed from the DOM. To cleanup subscriptions, we can return a `destructor` function from the subscription the same as in the `useEffect` hook.
+In the solution above `setInterval` will trigger events even if the component is removed from the DOM. To cleanup subscriptions, we can return a `destructor` function the same way as in the `useEffect` hook.
 
 Let's rewrite our `subscription` function:
 
 ```ts
 function subscription (model: Model): SubscriptionResult<Message> {
-    let timer: NodeJS.Timer;
+    const sub = (dispatch: Dispatch<Message>) => {
+        const timer = setInterval(() => dispatch(Msg.timer(new Date())), 1000);
 
-    const sub = (dispatch: Dispatch<Message>): void => {
-        timer = setInterval(() => dispatch(Msg.timer(new Date())), 1000);
-    }
-
-    const destructor = () => {
-        clearInterval(timer);
+        return () => {
+            clearInterval(timer);
+        }
     }
 
-    return [cmd.ofSub(sub), destructor];
+    return [sub];
 }
 ```
 
-Here we save the return value of `setInterval` and clear that interval in the returned `destructor` function.
+The destructor is called when the component is removed from the DOM.
 
 ## Setup
 

src/Testing/execSubscription.ts

@@ -1,6 +1,6 @@
 import type { Dispatch } from "react";
 import type { Message } from "../Types";
-import type { Subscription } from "../useElmish";
+import { subscriptionIsFunctionArray, type Subscription } from "../useElmish";
 import { execCmdWithDispatch } from "./execCmd";
 
 function execSubscription<TProps, TModel, TMessage extends Message>(
@@ -17,7 +17,19 @@ function execSubscription<TProps, TModel, TMessage extends Message>(
 		return noop;
 	}
 
-	const [cmd, dispose] = subscription(model, props);
+	const subscriptionResult = subscription(model, props);
+
+	if (subscriptionIsFunctionArray(subscriptionResult)) {
+		const disposers = subscriptionResult.map((sub) => sub(dispatch)).filter((disposer) => disposer !== undefined);
+
+		return () => {
+			for (const dispose of disposers) {
+				dispose();
+			}
+		};
+	}
+
+	const [cmd, dispose] = subscriptionResult;
 
 	execCmdWithDispatch<TMessage>(dispatch, cmd);
 

src/mergeSubscriptions.spec.ts

@@ -1,5 +1,4 @@
 import { cmd } from "./cmd";
-import { execCmd } from "./Common";
 import { mergeSubscriptions } from "./mergeSubscriptions";
 import type { Message } from "./Types";
 import type { SubscriptionResult } from "./useElmish";
@@ -47,10 +46,12 @@ describe("mergeSubscriptions", () => {
 		const sub2 = (): SubscriptionResult<Message> => [cmd.ofSub(sub2Fn)];
 
 		const subscription = mergeSubscriptions(sub1, sub2);
-		const [command] = subscription(model, props);
+		const commands = subscription(model, props);
 
 		// act
-		execCmd(mockDispatch, command);
+		for (const command of commands) {
+			command(mockDispatch);
+		}
 
 		// assert
 		expect(sub1Fn).toHaveBeenCalledWith(mockDispatch);
@@ -59,16 +60,20 @@ describe("mergeSubscriptions", () => {
 
 	it("executes all disposer functions", () => {
 		// arrange
+		const mockDispatch = jest.fn();
+
 		const dispose1 = jest.fn();
 		const sub1 = (): SubscriptionResult<Message> => [cmd.ofSub(jest.fn()), dispose1];
 		const dispose2 = jest.fn();
 		const sub2 = (): SubscriptionResult<Message> => [cmd.ofSub(jest.fn()), dispose2];
 
 		const subscription = mergeSubscriptions(sub1, sub2);
-		const [, dispose] = subscription(model, props);
+		const commands = subscription(model, props);
 
 		// act
-		dispose?.();
+		for (const command of commands) {
+			command(mockDispatch)?.();
+		}
 
 		// assert
 		expect(dispose1).toHaveBeenCalledTimes(1);

src/mergeSubscriptions.ts

@@ -1,24 +1,31 @@
-import { cmd } from "./cmd";
-import type { Message } from "./Types";
-import type { Subscription } from "./useElmish";
+import type { Dispatch, Message, Sub } from "./Types";
+import { subscriptionIsFunctionArray, type Subscription, type SubscriptionFunction } from "./useElmish";
+
+type MergedSubscription<TProps, TModel, TMessage> = (model: TModel, props: TProps) => SubscriptionFunction<TMessage>[];
 
 function mergeSubscriptions<TProps, TModel, TMessage extends Message>(
 	...subscriptions: (Subscription<TProps, TModel, TMessage> | undefined)[]
-): Subscription<TProps, TModel, TMessage> {
+): MergedSubscription<TProps, TModel, TMessage> {
 	return function mergedSubscription(model, props) {
-		const results = subscriptions.map((sub) => sub?.(model, props));
-
-		const commands = results.map((sub) => sub?.[0]);
-		const disposers = results.map((sub) => sub?.[1]);
-
-		return [
-			cmd.batch(...commands),
-			() => {
-				for (const disposer of disposers) {
-					disposer?.();
-				}
-			},
-		];
+		const results = subscriptions.map((sub) => sub?.(model, props)).filter((subscription) => subscription !== undefined);
+
+		const subscriptionFunctions = results.flatMap((result) => {
+			if (subscriptionIsFunctionArray(result)) {
+				return result;
+			}
+
+			const [subCmd, dispose] = result;
+
+			return [...subCmd.map(mapToFn), () => () => dispose?.()];
+		});
+
+		return subscriptionFunctions;
+	};
+}
+
+function mapToFn<TMessage>(cmd: Sub<TMessage>): (dispatch: Dispatch<TMessage>) => undefined {
+	return (dispatch) => {
+		cmd(dispatch);
 	};
 }
 

src/useElmish.ts

@@ -22,9 +22,14 @@ import { isReduxDevToolsEnabled, type ReduxDevTools } from "./reduxDevTools";
  * The return type of the `subscription` function.
  * @template TMessage The type of the messages discriminated union.
  */
-type SubscriptionResult<TMessage> = [Cmd<TMessage>, (() => void)?];
+type SubscriptionResult<TMessage> = [Cmd<TMessage>, (() => void)?] | SubscriptionFunction<TMessage>[];
+type SubscriptionFunction<TMessage> = (dispatch: Dispatch<TMessage>) => (() => void) | undefined;
 type Subscription<TProps, TModel, TMessage> = (model: TModel, props: TProps) => SubscriptionResult<TMessage>;
 
+function subscriptionIsFunctionArray(subscription: SubscriptionResult<unknown>): subscription is SubscriptionFunction<unknown>[] {
+	return typeof subscription[0] === "function";
+}
+
 /**
  * Options for the `useElmish` hook.
  * @interface UseElmishOptions
@@ -173,7 +178,19 @@ function useElmish<TProps, TModel, TMessage extends Message>({
 	// biome-ignore lint/correctness/useExhaustiveDependencies: We want to run this effect only once
 	useEffect(() => {
 		if (subscription) {
-			const [subCmd, destructor] = subscription(initializedModel, props);
+			const subscriptionResult = subscription(initializedModel, props);
+
+			if (subscriptionIsFunctionArray(subscriptionResult)) {
+				const destructors = subscriptionResult.map((sub) => sub(dispatch)).filter((destructor) => destructor !== undefined);
+
+				return function combinedDestructor() {
+					for (const destructor of destructors) {
+						destructor();
+					}
+				};
+			}
+
+			const [subCmd, destructor] = subscriptionResult;
 
 			execCmd(dispatch, subCmd);
 
@@ -239,6 +256,6 @@ function callUpdateMap<TProps, TModel, TMessage extends Message>(
 	return updateMap[msgName](msg, model, props, options);
 }
 
-export type { Subscription, SubscriptionResult, UseElmishOptions };
+export type { Subscription, SubscriptionFunction, SubscriptionResult, UseElmishOptions };
 
-export { callUpdate, callUpdateMap, useElmish };
+export { callUpdate, callUpdateMap, subscriptionIsFunctionArray, useElmish };