Replace uses of `hasOwnProperty.call` with simpler alternatives (#11009)

Three uses of `hasOwnProperty.call` have been replaced with simpler
alternatives. I did this because I found this convention confusing.

The `ComposableObservableStore` changes required adding a check for
whether the `config` is defined, because the old syntax would allow
iterating over `undefined` as if it was an empty object. Functionally
it should be identical. A new test was added to highlight this
functionality.

app/scripts/lib/ComposableObservableStore.js

@@ -13,8 +13,10 @@ export default class ComposableObservableStore extends ObservableStore {
    */
   constructor(initState, config) {
     super(initState);
+    if (config) {
       this.updateStructure(config);
     }
+  }
 
   /**
    * Composes a new internal store subscription structure
@@ -24,14 +26,12 @@ export default class ComposableObservableStore extends ObservableStore {
   updateStructure(config) {
     this.config = config;
     this.removeAllListeners();
-    for (const key in config) {
-      if (Object.prototype.hasOwnProperty.call(config, key)) {
+    for (const key of Object.keys(this.config)) {
       config[key].subscribe((state) => {
         this.updateState({ [key]: state });
       });
     }
   }
-  }
 
   /**
    * Merges all child store state into a single object rather than
@@ -40,16 +40,17 @@ export default class ComposableObservableStore extends ObservableStore {
    * @returns {Object} Object containing merged child store state
    */
   getFlatState() {
+    if (!this.config) {
+      return {};
+    }
     let flatState = {};
-    for (const key in this.config) {
-      if (Object.prototype.hasOwnProperty.call(this.config, key)) {
+    for (const key of Object.keys(this.config)) {
       const controller = this.config[key];
       const state = controller.getState
         ? controller.getState()
         : controller.state;
       flatState = { ...flatState, ...state };
     }
-    }
     return flatState;
   }
 }

app/scripts/lib/ComposableObservableStore.test.js

@@ -32,4 +32,9 @@ describe('ComposableObservableStore', function () {
     });
     assert.deepEqual(store.getFlatState(), { foo: 'foo', bar: 'bar' });
   });
+
+  it('should return empty flattened state when not configured', function () {
+    const store = new ComposableObservableStore();
+    assert.deepEqual(store.getFlatState(), {});
+  });
 });

app/scripts/lib/get-first-preferred-lang-code.js

@@ -40,9 +40,7 @@ export default async function getFirstPreferredLangCode() {
 
   const firstPreferredLangCode = userPreferredLocaleCodes
     .map((code) => code.toLowerCase().replace('_', '-'))
-    .find((code) =>
-      Object.prototype.hasOwnProperty.call(existingLocaleCodes, code),
-    );
+    .find((code) => existingLocaleCodes[code] !== undefined);
 
   return existingLocaleCodes[firstPreferredLangCode] || 'en';
 }