Adapt to useRef type changes

`useRef(null as T|null)` now returns a `{ current: T|null }` instead of
`{ current: T }` as it did before. ie. it no longer drops the the null.
This makes sense but conflicted with a pattern we used in many places to
create a non-null ref: `useRef(/** @type {T|null} */ (null))`.

Resolve this by changing all non-nullable refs, for elements which are
set after the initial render, to cast the `useRef` result instead of the
init value.

```
const nonNullRef = /** @type {{ current: T }} */ (useRef());
```

src/annotator/components/NotebookModal.js

@@ -33,6 +33,8 @@ function NotebookIframe({ config, groupId }) {
   );
 }
 
+/** @typedef {import('../util/emitter').Emitter} Emitter */
+
 /**
  * @typedef NotebookModalProps
  * @prop {import('../util/emitter').EventBus} eventBus
@@ -53,9 +55,7 @@ export default function NotebookModal({ eventBus, config }) {
   const [isHidden, setIsHidden] = useState(true);
   const [groupId, setGroupId] = useState(/** @type {string|null} */ (null));
   const originalDocumentOverflowStyle = useRef('');
-  const emitter = useRef(
-    /** @type {ReturnType<eventBus['createEmitter']>|null} */ (null)
-  );
+  const emitterRef = useRef(/** @type {Emitter|null} */ (null));
 
   // Stores the original overflow CSS property of document.body and reset it
   // when the component is destroyed
@@ -78,24 +78,22 @@ export default function NotebookModal({ eventBus, config }) {
   }, [isHidden]);
 
   useEffect(() => {
-    emitter.current = eventBus.createEmitter();
-    emitter.current.subscribe(
-      'openNotebook',
-      (/** @type {string} */ groupId) => {
-        setIsHidden(false);
-        setIframeKey(iframeKey => iframeKey + 1);
-        setGroupId(groupId);
-      }
-    );
+    const emitter = eventBus.createEmitter();
+    emitter.subscribe('openNotebook', (/** @type {string} */ groupId) => {
+      setIsHidden(false);
+      setIframeKey(iframeKey => iframeKey + 1);
+      setGroupId(groupId);
+    });
+    emitterRef.current = emitter;
 
     return () => {
-      emitter.current.destroy();
+      emitter.destroy();
     };
   }, [eventBus]);
 
   const onClose = () => {
     setIsHidden(true);
-    emitter.current.publish('closeNotebook');
+    emitterRef.current?.publish('closeNotebook');
   };
 
   if (groupId === null) {

src/annotator/util/emitter.js

@@ -10,7 +10,7 @@ import { TinyEmitter } from 'tiny-emitter';
  *
  * @implements Destroyable
  */
-class Emitter {
+export class Emitter {
   /**
    * @param {TinyEmitter} emitter
    */

src/sidebar/components/Annotation/AnnotationShareControl.js

@@ -60,6 +60,9 @@ function AnnotationShareControl({
   const closePanel = () => setOpen(false);
 
   // Interactions outside of the component when it is open should close it
+  //
+  // @ts-expect-error - `useElementShouldClose` requires a non-nullable ref,
+  // but `shareRef` is nullable.
   useElementShouldClose(shareRef, isOpen, closePanel);
 
   useEffect(() => {

src/sidebar/components/Excerpt.js

@@ -87,7 +87,7 @@ function Excerpt({
     useState(true);
 
   // Container for the excerpt's content.
-  const contentElement = useRef(/** @type {HTMLDivElement|null} */ (null));
+  const contentElement = /** @type {{ current: HTMLDivElement }} */ (useRef());
 
   // Measured height of `contentElement` in pixels.
   const [contentHeight, setContentHeight] = useState(0);

src/sidebar/components/MarkdownEditor.js

@@ -402,15 +402,16 @@ export default function MarkdownEditor({
 
   useEffect(() => {
     if (!preview) {
-      input.current.focus();
+      input.current?.focus();
     }
   }, [preview]);
 
   const togglePreview = () => setPreview(!preview);
   const handleCommand = command => {
-    const inputEl = input.current;
-    handleToolbarCommand(command, inputEl);
-    onEditText({ text: inputEl.value });
+    if (input.current) {
+      handleToolbarCommand(command, input.current);
+      onEditText({ text: input.current.value });
+    }
   };
 
   const handleKeyDown = event => {

src/sidebar/components/MarkdownView.js

@@ -28,7 +28,7 @@ export default function MarkdownView({
     () => (markdown ? renderMarkdown(markdown) : ''),
     [markdown]
   );
-  const content = useRef(/** @type {HTMLDivElement|null} */ (null));
+  const content = /** @type {{ current: HTMLDivElement }} */ (useRef());
 
   useEffect(() => {
     replaceLinksWithEmbeds(content.current, {

src/sidebar/components/Menu.js

@@ -138,7 +138,7 @@ export default function Menu({
   //
   // These handlers close the menu when the user taps or clicks outside the
   // menu or presses Escape.
-  const menuRef = useRef(/** @type {HTMLDivElement|null} */ (null));
+  const menuRef = /** @type {{ current: HTMLDivElement }} */ (useRef());
 
   // Menu element should close via `closeMenu` whenever it's open and there
   // are user interactions outside of it (e.g. clicks) in the document

src/sidebar/components/MenuItem.js

@@ -81,9 +81,9 @@ export default function MenuItem({
   const hasLeftIcon = icon || isSubmenuItem;
   const hasRightIcon = icon && isSubmenuItem;
 
-  const menuItemRef = useRef(
-    /** @type {(HTMLAnchorElement & HTMLDivElement)|null} */ (null)
-  );
+  const menuItemRef =
+    /** @type {{ current: HTMLAnchorElement & HTMLDivElement }} */ (useRef());
+
   let focusTimer = null;
 
   let renderedIcon = null;

src/sidebar/components/MenuKeyboardNavigation.js

@@ -28,7 +28,7 @@ export default function MenuKeyboardNavigation({
   children,
   visible,
 }) {
-  const menuRef = useRef(/** @type {HTMLDivElement|null} */ (null));
+  const menuRef = /** @type {{ current: HTMLDivElement }} */ (useRef());
 
   useEffect(() => {
     let focusTimer = null;

src/sidebar/components/SearchInput.js

@@ -28,7 +28,7 @@ import { useStoreProxy } from '../store/use-store';
 export default function SearchInput({ alwaysExpanded, query, onSearch }) {
   const store = useStoreProxy();
   const isLoading = store.isLoading();
-  const input = useRef(/** @type {HTMLInputElement|null} */ (null));
+  const input = /** @type {{ current: HTMLInputElement }} */ (useRef());
 
   // The active filter query from the previous render.
   const [prevQuery, setPrevQuery] = useState(query);

src/sidebar/components/Slider.js

@@ -19,7 +19,7 @@ import { useCallback, useEffect, useRef, useState } from 'preact/hooks';
  * @param {SliderProps} props
  */
 export default function Slider({ children, visible }) {
-  const containerRef = useRef(/** @type {HTMLDivElement|null} */ (null));
+  const containerRef = /** @type {{ current: HTMLDivElement }} */ (useRef());
   const [containerHeight, setContainerHeight] = useState(visible ? 'auto' : 0);
 
   // Whether the content is currently partially or wholly visible. This is

src/sidebar/components/TagEditor.js

@@ -38,7 +38,7 @@ function TagEditor({
   tagList,
   tags: tagsService,
 }) {
-  const inputEl = useRef(/** @type {HTMLInputElement|null} */ (null));
+  const inputEl = /** @type {{ current: HTMLInputElement }} */ (useRef());
   const [suggestions, setSuggestions] = useState(/** @type {string[]} */ ([]));
   const [activeItem, setActiveItem] = useState(-1); // -1 is unselected
   const [suggestionsListOpen, setSuggestionsListOpen] = useState(false);
@@ -48,7 +48,7 @@ function TagEditor({
   });
 
   // Set up callback to monitor outside click events to close the AutocompleteList
-  const closeWrapperRef = useRef(/** @type {HTMLElement|null} */ (null));
+  const closeWrapperRef = /** @type {{ current: HTMLElement }} */ (useRef());
   useElementShouldClose(closeWrapperRef, suggestionsListOpen, () => {
     setSuggestionsListOpen(false);
   });

src/sidebar/store/use-store.js

@@ -144,5 +144,5 @@ export function useStoreProxy() {
     return cleanup;
   }, [cache, store]);
 
-  return proxy.current;
+  return /** @type {SidebarStore} */ (proxy.current);
 }