Bug 1661671 - Add plugin to support optional chaining operator in unit tests r=k88hudson

Differential Revision: https://phabricator.services.mozilla.com/D88581

browser/components/newtab/aboutwelcome/AboutWelcomeChild.jsm

@@ -238,7 +238,7 @@ class AboutWelcomeChild extends JSWindowActorChild {
       Cu.reportError(e);
     }
 
-    if (experimentData && experimentData.slug) {
+    if (experimentData?.slug) {
       log.debug(
         `Loading about:welcome with experiment: ${experimentData.slug}`
       );

browser/components/newtab/aboutwelcome/content/aboutwelcome.bundle.js

@@ -224,9 +224,9 @@ async function mount() {
     slug,
     branch
   } = await window.AWGetStartupData();
-  let settings = branch && branch.feature ? branch.feature.value : {};
+  let settings = (branch === null || branch === void 0 ? void 0 : branch.feature) ? branch.feature.value : {};
 
-  if (!(branch && branch.feature)) {
+  if (!(branch === null || branch === void 0 ? void 0 : branch.feature)) {
     // Check for override content in pref browser.aboutwelcome.overrideContent
     settings = await window.AWGetMultiStageScreens();
   }

browser/components/newtab/content-src/aboutwelcome/aboutwelcome.jsx

@@ -117,9 +117,9 @@ function ComputeMessageId(experimentId, branchId, settings) {
 
 async function mount() {
   const { slug, branch } = await window.AWGetStartupData();
-  let settings = branch && branch.feature ? branch.feature.value : {};
+  let settings = branch?.feature ? branch.feature.value : {};
 
-  if (!(branch && branch.feature)) {
+  if (!branch?.feature) {
     // Check for override content in pref browser.aboutwelcome.overrideContent
     settings = await window.AWGetMultiStageScreens();
   }

browser/components/newtab/lib/ASRouter.jsm

@@ -362,11 +362,7 @@ const MessageLoaderUtils = {
         continue;
       }
 
-      if (
-        experimentData &&
-        experimentData.branch &&
-        experimentData.branch.feature
-      ) {
+      if (experimentData?.branch?.feature) {
         experiments.push(experimentData.branch.feature.value);
 
         if (!REACH_EVENT_GROUPS.includes(featureId)) {

browser/components/newtab/webpack.system-addon.config.js

@@ -33,6 +33,7 @@ module.exports = (env = {}) => ({
         loader: "babel-loader",
         options: {
           presets: ["@babel/preset-react"],
+          plugins: ["@babel/plugin-proposal-optional-chaining"],
         },
       },
       {