Fix typechecking errors in src/annotator/{index, pdf-sidebar}

CoffeeScript imports are marked as expected errors for the moment. They
will be checked once those files are converted.

src/annotator/index.js

 /* global process */
 
+/**
+ * @typedef {import('../types/annotator').HypothesisWindow} HypothesisWindow
+ */
+
 import $ from 'jquery';
 
 // Load polyfill for :focus-visible pseudo-class.
@@ -16,12 +20,20 @@ import iconSet from './icons';
 registerIcons(iconSet);
 
 import configFrom from './config/index';
-import Guest from './guest';
 import PdfSidebar from './pdf-sidebar';
+import DocumentPlugin from './plugin/document';
+
+// Modules that are still written in CoffeeScript and need to be converted to
+// JS.
+// @ts-expect-error
+import Guest from './guest';
+// @ts-expect-error
 import BucketBarPlugin from './plugin/bucket-bar';
+// @ts-expect-error
 import CrossFramePlugin from './plugin/cross-frame';
-import DocumentPlugin from './plugin/document';
+// @ts-expect-error
 import PDFPlugin from './plugin/pdf';
+// @ts-expect-error
 import Sidebar from './sidebar';
 
 const pluginClasses = {
@@ -36,13 +48,20 @@ const pluginClasses = {
   CrossFrame: CrossFramePlugin,
 };
 
-const appLinkEl = document.querySelector(
+const window_ = /** @type {HypothesisWindow} */ (window);
+
+// Look up the URL of the sidebar. This element is added to the page by the
+// boot script before the "annotator" bundle loads.
+const appLinkEl = /** @type {Element} */ (document.querySelector(
   'link[type="application/annotator+html"][rel="sidebar"]'
-);
+));
+
 const config = configFrom(window);
 
 $.noConflict(true)(function () {
-  let Klass = window.PDFViewerApplication ? PdfSidebar : Sidebar;
+  const isPDF = typeof window_.PDFViewerApplication !== 'undefined';
+
+  let Klass = isPDF ? PdfSidebar : Sidebar;
 
   if (config.hasOwnProperty('constructor')) {
     Klass = config.constructor;
@@ -51,7 +70,7 @@ $.noConflict(true)(function () {
 
   if (config.subFrameIdentifier) {
     // Make sure the PDF plugin is loaded if the subframe contains the PDF.js viewer.
-    if (typeof window.PDFViewerApplication !== 'undefined') {
+    if (isPDF) {
       config.PDF = {};
     }
     Klass = Guest;
@@ -59,14 +78,14 @@ $.noConflict(true)(function () {
     // Other modules use this to detect if this
     // frame context belongs to hypothesis.
     // Needs to be a global property that's set.
-    window.__hypothesis_frame = true;
+    window_.__hypothesis_frame = true;
   }
 
   config.pluginClasses = pluginClasses;
 
   const annotator = new Klass(document.body, config);
   appLinkEl.addEventListener('destroy', function () {
-    appLinkEl.parentElement.removeChild(appLinkEl);
+    appLinkEl.remove();
     annotator.destroy();
   });
 });

src/annotator/pdf-sidebar.js

+// @ts-expect-error - './sidebar' needs to be converted from JS.
 import Sidebar from './sidebar';
 
 const DEFAULT_CONFIG = {

src/types/annotator.js

@@ -32,5 +32,20 @@
  * @prop {string} [documentFingerprint]
  */
 
+/**
+ * Global variables which the Hypothesis client looks for on the `window` object
+ * when loaded in a frame that influence how it behaves.
+ *
+ * @typedef Globals
+ * @prop {Object} [PDFViewerApplication] -
+ *   PDF.js entry point. If set triggers loading of PDF rather than HTML integration.
+ * @prop {boolean} [__hypothesis_frame] -
+ *   Flag used to indicate that Hypothesis is loaded in the current frame.
+ */
+
+/**
+ * @typedef {Window & Globals} HypothesisWindow
+ */
+
 // Make TypeScript treat this file as a module.
 export const unused = {};