Add types for "defaults" store module

src/sidebar/services/persisted-defaults.js

 import { watch } from '../util/watch';
 
+/**
+ * @typedef {import('../store/modules/defaults').Key} Key
+ */
+
+/** @type {Record<Key, string>} */
 const DEFAULT_KEYS = {
   annotationPrivacy: 'hypothesis.privacy',
   focusedGroup: 'hypothesis.groups.focus',
@@ -46,7 +51,7 @@ export class PersistedDefaultsService {
     Object.keys(DEFAULT_KEYS).forEach(defaultKey => {
       // `localStorage.getItem` will return `null` for a non-existent key
       const defaultValue = this._storage.getItem(DEFAULT_KEYS[defaultKey]);
-      this._store.setDefault(defaultKey, defaultValue);
+      this._store.setDefault(/** @type {Key} */ (defaultKey), defaultValue);
     });
 
     // Listen for changes to those defaults from the store and persist them

src/sidebar/store/modules/defaults.js

-import * as util from '../util';
-
-import { createStoreModule } from '../create-store';
+import { createStoreModule, makeAction } from '../create-store';
 
 /**
  * A store module for managing client-side user-convenience defaults.
@@ -21,16 +19,27 @@ const initialState = {
   focusedGroup: /** @type {string|null} */ (null),
 };
 
+/**
+ * @typedef {keyof initialState} Key
+ * @typedef {typeof initialState} State
+ */
+
 const reducers = {
-  SET_DEFAULT: function (state, action) {
+  /**
+   * @param {State} state
+   * @param {{ defaultKey: Key, value: string|null }} action
+   */
+  SET_DEFAULT(state, action) {
     return { [action.defaultKey]: action.value };
   },
 };
 
-const actions = util.actionTypes(reducers);
-
+/**
+ * @param {Key} defaultKey
+ * @param {string|null} value
+ */
 function setDefault(defaultKey, value) {
-  return { type: actions.SET_DEFAULT, defaultKey, value };
+  return makeAction(reducers, 'SET_DEFAULT', { defaultKey, value });
 }
 
 /** Selectors */
@@ -38,13 +47,14 @@ function setDefault(defaultKey, value) {
 /**
  * Retrieve the state's current value for `defaultKey`.
  *
- * @return {string|null} - The current value for `defaultKey` or `undefined` if it is not
- *               present
+ * @param {State} state
+ * @param {Key} defaultKey
  */
 function getDefault(state, defaultKey) {
   return state[defaultKey];
 }
 
+/** @param {State} state */
 function getDefaults(state) {
   return state;
 }