Create Room Name & Topic HOCs to simplify code elsewhere

src/components/views/elements/RoomTopic.tsx

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+/*
+Copyright 2021 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 React, {useEffect, useState} from "react";
+import {EventType} from "matrix-js-sdk/src/@types/event";
+import {Room} from "matrix-js-sdk/src/models/room";
+
+import {useEventEmitter} from "../../../hooks/useEventEmitter";
+import {linkifyElement} from "../../../HtmlUtils";
+
+interface IProps {
+    room?: Room;
+    children?(topic: string, ref: (element: HTMLElement) => void): JSX.Element;
+}
+
+export const getTopic = room => room?.currentState?.getStateEvents(EventType.RoomTopic, "")?.getContent()?.topic;
+
+const RoomTopic = ({ room, children }: IProps): JSX.Element => {
+    const [topic, setTopic] = useState(getTopic(room));
+    useEventEmitter(room.currentState, "RoomState.events", () => {
+        setTopic(getTopic(room));
+    });
+    useEffect(() => {
+        setTopic(getTopic(room));
+    }, [room]);
+
+    const ref = e => e && linkifyElement(e);
+    if (children) return children(topic, ref);
+    return <span ref={ref}>{ topic }</span>;
+};
+
+export default RoomTopic;