diff --git a/external/builder/babel-plugin-pdfjs-preprocessor.mjs b/external/builder/babel-plugin-pdfjs-preprocessor.mjs
index 87b024bab..945d22c47 100644
--- a/external/builder/babel-plugin-pdfjs-preprocessor.mjs
+++ b/external/builder/babel-plugin-pdfjs-preprocessor.mjs
@@ -11,7 +11,7 @@ function isPDFJSPreprocessor(obj) {
 }
 
 function evalWithDefines(code, defines) {
-  if (!code || !code.trim()) {
+  if (!code?.trim()) {
     throw new Error("No JavaScript expression given");
   }
   return vm.runInNewContext(code, defines, { displayErrors: false });
@@ -56,12 +56,7 @@ function handlePreprocessorAction(ctx, actionName, args, path) {
     throw new Error("Unsupported action");
   } catch (e) {
     throw path.buildCodeFrameError(
-      "Could not process " +
-        PDFJS_PREPROCESSOR_NAME +
-        "." +
-        actionName +
-        ": " +
-        e.message
+      `Could not process ${PDFJS_PREPROCESSOR_NAME}.${actionName}: ${e.message}`
     );
   }
 }
diff --git a/external/builder/builder.mjs b/external/builder/builder.mjs
index 783ef9b30..929a9cf87 100644
--- a/external/builder/builder.mjs
+++ b/external/builder/builder.mjs
@@ -84,7 +84,7 @@ function preprocess(inFilename, outFilename, defines) {
           out.push(line);
         };
   function evaluateCondition(code) {
-    if (!code || !code.trim()) {
+    if (!code?.trim()) {
       throw new Error("No JavaScript expression given at " + loc());
     }
     try {
diff --git a/gulpfile.mjs b/gulpfile.mjs
index b3650472f..b4676c250 100644
--- a/gulpfile.mjs
+++ b/gulpfile.mjs
@@ -124,9 +124,8 @@ function transform(charEncoding, transformFunction) {
   });
 }
 
-function safeSpawnSync(command, parameters, options) {
+function safeSpawnSync(command, parameters, options = {}) {
   // Execute all commands in a shell.
-  options = options || {};
   options.shell = true;
   // `options.shell = true` requires parameters to be quoted.
   parameters = parameters.map(param => {
@@ -175,6 +174,87 @@ function createStringSource(filename, content) {
   return source;
 }
 
+function createWebpackAlias(defines) {
+  const basicAlias = {
+    pdfjs: "src",
+    "pdfjs-web": "web",
+    "pdfjs-lib": "web/pdfjs",
+    "fluent-bundle": "node_modules/@fluent/bundle/esm/index.js",
+    "fluent-dom": "node_modules/@fluent/dom/esm/index.js",
+  };
+  const libraryAlias = {
+    "display-fetch_stream": "src/display/stubs.js",
+    "display-network": "src/display/stubs.js",
+    "display-node_stream": "src/display/stubs.js",
+    "display-node_utils": "src/display/stubs.js",
+  };
+  const viewerAlias = {
+    "web-alt_text_manager": "web/alt_text_manager.js",
+    "web-annotation_editor_params": "web/annotation_editor_params.js",
+    "web-download_manager": "",
+    "web-external_services": "",
+    "web-null_l10n": "",
+    "web-pdf_attachment_viewer": "web/pdf_attachment_viewer.js",
+    "web-pdf_cursor_tools": "web/pdf_cursor_tools.js",
+    "web-pdf_document_properties": "web/pdf_document_properties.js",
+    "web-pdf_find_bar": "web/pdf_find_bar.js",
+    "web-pdf_layer_viewer": "web/pdf_layer_viewer.js",
+    "web-pdf_outline_viewer": "web/pdf_outline_viewer.js",
+    "web-pdf_presentation_mode": "web/pdf_presentation_mode.js",
+    "web-pdf_sidebar": "web/pdf_sidebar.js",
+    "web-pdf_thumbnail_viewer": "web/pdf_thumbnail_viewer.js",
+    "web-preferences": "",
+    "web-print_service": "",
+    "web-secondary_toolbar": "web/secondary_toolbar.js",
+    "web-toolbar": "web/toolbar.js",
+  };
+
+  if (defines.CHROME) {
+    libraryAlias["display-fetch_stream"] = "src/display/fetch_stream.js";
+    libraryAlias["display-network"] = "src/display/network.js";
+
+    viewerAlias["web-download_manager"] = "web/download_manager.js";
+    viewerAlias["web-external_services"] = "web/chromecom.js";
+    viewerAlias["web-null_l10n"] = "web/l10n.js";
+    viewerAlias["web-preferences"] = "web/chromecom.js";
+    viewerAlias["web-print_service"] = "web/pdf_print_service.js";
+  } else if (defines.GENERIC) {
+    // Aliases defined here must also be replicated in the paths section of
+    // the tsconfig.json file for the type generation to work.
+    // In the tsconfig.json files, the .js extension must be omitted.
+    libraryAlias["display-fetch_stream"] = "src/display/fetch_stream.js";
+    libraryAlias["display-network"] = "src/display/network.js";
+    libraryAlias["display-node_stream"] = "src/display/node_stream.js";
+    libraryAlias["display-node_utils"] = "src/display/node_utils.js";
+
+    viewerAlias["web-download_manager"] = "web/download_manager.js";
+    viewerAlias["web-external_services"] = "web/genericcom.js";
+    viewerAlias["web-null_l10n"] = "web/genericl10n.js";
+    viewerAlias["web-preferences"] = "web/genericcom.js";
+    viewerAlias["web-print_service"] = "web/pdf_print_service.js";
+  } else if (defines.MOZCENTRAL) {
+    if (defines.GECKOVIEW) {
+      const gvAlias = {
+        "web-toolbar": "web/toolbar-geckoview.js",
+      };
+      for (const key in viewerAlias) {
+        viewerAlias[key] = gvAlias[key] || "web/stubs-geckoview.js";
+      }
+    }
+    viewerAlias["web-download_manager"] = "web/firefoxcom.js";
+    viewerAlias["web-external_services"] = "web/firefoxcom.js";
+    viewerAlias["web-null_l10n"] = "web/l10n.js";
+    viewerAlias["web-preferences"] = "web/firefoxcom.js";
+    viewerAlias["web-print_service"] = "web/firefox_print_service.js";
+  }
+
+  const alias = { ...basicAlias, ...libraryAlias, ...viewerAlias };
+  for (const key in alias) {
+    alias[key] = path.join(__dirname, alias[key]);
+  }
+  return alias;
+}
+
 function createWebpackConfig(
   defines,
   output,
@@ -251,87 +331,12 @@ function createWebpackConfig(
     );
   }
 
+  const alias = createWebpackAlias(bundleDefines);
   const experiments = isModule ? { outputModule: true } : undefined;
 
   // Required to expose e.g., the `window` object.
   output.globalObject = "globalThis";
 
-  const basicAlias = {
-    pdfjs: "src",
-    "pdfjs-web": "web",
-    "pdfjs-lib": "web/pdfjs",
-    "fluent-bundle": "node_modules/@fluent/bundle/esm/index.js",
-    "fluent-dom": "node_modules/@fluent/dom/esm/index.js",
-  };
-  const libraryAlias = {
-    "display-fetch_stream": "src/display/stubs.js",
-    "display-network": "src/display/stubs.js",
-    "display-node_stream": "src/display/stubs.js",
-    "display-node_utils": "src/display/stubs.js",
-  };
-  const viewerAlias = {
-    "web-alt_text_manager": "web/alt_text_manager.js",
-    "web-annotation_editor_params": "web/annotation_editor_params.js",
-    "web-download_manager": "",
-    "web-external_services": "",
-    "web-null_l10n": "",
-    "web-pdf_attachment_viewer": "web/pdf_attachment_viewer.js",
-    "web-pdf_cursor_tools": "web/pdf_cursor_tools.js",
-    "web-pdf_document_properties": "web/pdf_document_properties.js",
-    "web-pdf_find_bar": "web/pdf_find_bar.js",
-    "web-pdf_layer_viewer": "web/pdf_layer_viewer.js",
-    "web-pdf_outline_viewer": "web/pdf_outline_viewer.js",
-    "web-pdf_presentation_mode": "web/pdf_presentation_mode.js",
-    "web-pdf_sidebar": "web/pdf_sidebar.js",
-    "web-pdf_thumbnail_viewer": "web/pdf_thumbnail_viewer.js",
-    "web-preferences": "",
-    "web-print_service": "",
-    "web-secondary_toolbar": "web/secondary_toolbar.js",
-    "web-toolbar": "web/toolbar.js",
-  };
-  if (bundleDefines.CHROME) {
-    libraryAlias["display-fetch_stream"] = "src/display/fetch_stream.js";
-    libraryAlias["display-network"] = "src/display/network.js";
-
-    viewerAlias["web-download_manager"] = "web/download_manager.js";
-    viewerAlias["web-external_services"] = "web/chromecom.js";
-    viewerAlias["web-null_l10n"] = "web/l10n.js";
-    viewerAlias["web-preferences"] = "web/chromecom.js";
-    viewerAlias["web-print_service"] = "web/pdf_print_service.js";
-  } else if (bundleDefines.GENERIC) {
-    // Aliases defined here must also be replicated in the paths section of
-    // the tsconfig.json file for the type generation to work.
-    // In the tsconfig.json files, the .js extension must be omitted.
-    libraryAlias["display-fetch_stream"] = "src/display/fetch_stream.js";
-    libraryAlias["display-network"] = "src/display/network.js";
-    libraryAlias["display-node_stream"] = "src/display/node_stream.js";
-    libraryAlias["display-node_utils"] = "src/display/node_utils.js";
-
-    viewerAlias["web-download_manager"] = "web/download_manager.js";
-    viewerAlias["web-external_services"] = "web/genericcom.js";
-    viewerAlias["web-null_l10n"] = "web/genericl10n.js";
-    viewerAlias["web-preferences"] = "web/genericcom.js";
-    viewerAlias["web-print_service"] = "web/pdf_print_service.js";
-  } else if (bundleDefines.MOZCENTRAL) {
-    if (bundleDefines.GECKOVIEW) {
-      const gvAlias = {
-        "web-toolbar": "web/toolbar-geckoview.js",
-      };
-      for (const key in viewerAlias) {
-        viewerAlias[key] = gvAlias[key] || "web/stubs-geckoview.js";
-      }
-    }
-    viewerAlias["web-download_manager"] = "web/firefoxcom.js";
-    viewerAlias["web-external_services"] = "web/firefoxcom.js";
-    viewerAlias["web-null_l10n"] = "web/l10n.js";
-    viewerAlias["web-preferences"] = "web/firefoxcom.js";
-    viewerAlias["web-print_service"] = "web/firefox_print_service.js";
-  }
-  const alias = { ...basicAlias, ...libraryAlias, ...viewerAlias };
-  for (const key in alias) {
-    alias[key] = path.join(__dirname, alias[key]);
-  }
-
   return {
     mode: "production",
     optimization: {
@@ -404,7 +409,7 @@ function checkChromePreferencesFile(chromePrefsPath, webPrefs) {
     // Deprecated keys are allowed in the managed preferences file.
     // The code maintainer is responsible for adding migration logic to
     // extensions/chromium/options/migration.js and web/chromecom.js .
-    return !description || !description.startsWith("DEPRECATED.");
+    return !description?.startsWith("DEPRECATED.");
   });
 
   let ret = true;
@@ -514,7 +519,7 @@ function createSandboxExternal(defines) {
 
 function createTemporaryScriptingBundle(defines, extraOptions = undefined) {
   return createScriptingBundle(defines, {
-    disableVersionInfo: !!(extraOptions && extraOptions.disableVersionInfo),
+    disableVersionInfo: !!extraOptions?.disableVersionInfo,
     disableSourceMaps: true,
     disableLicenseHeader: true,
   }).pipe(gulp.dest(TMP_DIR));