Enable import/extensions of ESlint plugin to enforce all import hav…

…e a `.js` file extension.

Related to mozilla#11465.

- https://github.com/benmosher/eslint-plugin-import/blob/master/docs/rules/extensions.md

.eslintrc

@@ -31,6 +31,7 @@
 
  "rules": {
  // Plugins
+ "import/extensions": ["error", "always", { "ignorePackages": true }],
  "import/no-unresolved": "error",
  "mozilla/avoid-removeChild": "error",
  "mozilla/use-includes-instead-of-indexOf": "error",

src/shared/util.js

@@ -14,7 +14,7 @@
  */
 /* eslint no-var: error */
 
-import "./compatibility";
+import "./compatibility.js";
 
 const IDENTITY_MATRIX = [1, 0, 0, 1, 0, 0];
 const FONT_IDENTITY_MATRIX = [0.001, 0, 0, 0.001, 0, 0];

web/firefoxcom.js

@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-import "../extensions/firefox/tools/l10n";
+import "../extensions/firefox/tools/l10n.js";
 import { createObjectURL, PDFDataRangeTransport, shadow } from "pdfjs-lib";
 import { BasePreferences } from "./preferences.js";
 import { DEFAULT_SCALE_VALUE } from "./ui_utils.js";

web/genericl10n.js

@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-import "../external/webL10n/l10n";
+import "../external/webL10n/l10n.js";
 
 const webL10n = document.webL10n;