Migrate AutoHideScrollbar to TypeScript

Also changed the way the React.RefObject is collected

src/components/structures/AutoHideScrollbar.tsx

@@ -0,0 +1,65 @@
+/*
+Copyright 2018 New Vector Ltd
+Copyright 2020 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 from "react";
+
+interface IProps {
+    className?: string;
+    onScroll?: () => void;
+    onWheel?: () => void;
+    style?: React.CSSProperties
+    tabIndex?: number,
+    wrappedRef?: (ref: HTMLDivElement) => void;
+}
+
+export default class AutoHideScrollbar extends React.Component<IProps> {
+    private containerRef: React.RefObject<HTMLDivElement> = React.createRef();
+
+    componentDidMount() {
+        if (this.containerRef.current && this.props.onScroll) {
+            // Using the passive option to not block the main thread
+            // https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#improving_scrolling_performance_with_passive_listeners
+            this.containerRef.current.addEventListener("scroll", this.props.onScroll, { passive: true });
+        }
+
+        if (this.props.wrappedRef) {
+            this.props.wrappedRef(this.containerRef.current);
+        }
+    }
+
+    componentWillUnmount() {
+        if (this.containerRef.current && this.props.onScroll) {
+            this.containerRef.current.removeEventListener("scroll", this.props.onScroll);
+        }
+    }
+
+    getScrollTop() {
+        return this.containerRef.current.scrollTop;
+    }
+
+    render() {
+        return (<div
+            ref={this.containerRef}
+            style={this.props.style}
+            className={["mx_AutoHideScrollbar", this.props.className].join(" ")}
+            onWheel={this.props.onWheel}
+            tabIndex={this.props.tabIndex}
+        >
+            { this.props.children }
+        </div>);
+    }
+}