Convert `threads` service to an ES class

Part of https://github.com/hypothesis/client/issues/3298

src/sidebar/components/Thread.js

@@ -14,7 +14,7 @@ import ModerationBanner from './ModerationBanner';
 /**
  * @typedef ThreadProps
  * @prop {Thread} thread
- * @prop {Object} threadsService - Injected service
+ * @prop {import('../services/threads').ThreadsService} threadsService
  */
 
 /**

src/sidebar/index.js

@@ -112,7 +112,7 @@ import sessionService from './services/session';
 import { StreamFilter } from './services/stream-filter';
 import streamerService from './services/streamer';
 import tagsService from './services/tags';
-import threadsService from './services/threads';
+import { ThreadsService } from './services/threads';
 import { ToastMessengerService } from './services/toast-messenger';
 
 // Redux store.
@@ -150,7 +150,7 @@ function startApp(config, appEl) {
     .register('streamer', streamerService)
     .register('streamFilter', StreamFilter)
     .register('tags', tagsService)
-    .register('threadsService', threadsService)
+    .register('threadsService', ThreadsService)
     .register('toastMessenger', ToastMessengerService)
     .register('store', store);
 

src/sidebar/services/test/threads-test.js

-import threadsService from '../threads';
+import { ThreadsService } from '../threads';
 
 const NESTED_THREADS = {
   id: 'top',
@@ -60,7 +60,7 @@ const NESTED_THREADS = {
   ],
 };
 
-describe('threadsService', () => {
+describe('ThreadsService', () => {
   let fakeStore;
   let service;
 
@@ -68,7 +68,7 @@ describe('threadsService', () => {
     fakeStore = {
       setForcedVisible: sinon.stub(),
     };
-    service = threadsService(fakeStore);
+    service = new ThreadsService(fakeStore);
   });
 
   describe('#forceVisible', () => {

src/sidebar/services/threads.js

@@ -2,8 +2,18 @@
  * @typedef {import('../helpers/build-thread').Thread} Thread
  */
 
+/**
+ * A service for performing operations related to the current set of threads.
+ */
 // @inject
-export default function threadsService(store) {
+export class ThreadsService {
+  /**
+   * @param {import('../store').SidebarStore} store
+   */
+  constructor(store) {
+    this._store = store;
+  }
+
   /**
    * Make this thread and all of its children "visible". This has the effect of
    * "unhiding" a thread which is currently hidden by an applied search filter
@@ -12,16 +22,12 @@ export default function threadsService(store) {
    *
    * @param {Thread} thread
    */
-  function forceVisible(thread) {
+  forceVisible(thread) {
     thread.children.forEach(child => {
-      forceVisible(child);
+      this.forceVisible(child);
     });
     if (!thread.visible) {
-      store.setForcedVisible(thread.id, true);
+      this._store.setForcedVisible(thread.id, true);
     }
   }
-
-  return {
-    forceVisible,
-  };
 }