Convert hooks to Typescript

src/hooks/useEventEmitter.ts

@@ -0,0 +1,50 @@
+/*
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {useRef, useEffect} from "react";
+import type {EventEmitter} from "events";
+
+type Handler = (...args: any[]) => void;
+
+// Hook to wrap event emitter on and removeListener in hook lifecycle
+export const useEventEmitter = (emitter: EventEmitter, eventName: string | symbol, handler: Handler) => {
+    // Create a ref that stores handler
+    const savedHandler = useRef(handler);
+
+    // Update ref.current value if handler changes.
+    useEffect(() => {
+        savedHandler.current = handler;
+    }, [handler]);
+
+    useEffect(
+        () => {
+            // allow disabling this hook by passing a falsy emitter
+            if (!emitter) return;
+
+            // Create event listener that calls handler function stored in ref
+            const eventListener = (...args) => savedHandler.current(...args);
+
+            // Add event listener
+            emitter.on(eventName, eventListener);
+
+            // Remove event listener on cleanup
+            return () => {
+                emitter.removeListener(eventName, eventListener);
+            };
+        },
+        [eventName, emitter], // Re-run if eventName or emitter changes
+    );
+};