Fix a bunch of ESLint and HTMLLint errors

frontend/src/.eslintrc.yml

@@ -0,0 +1,3 @@
+env:
+  browser: true
+  jquery: true

frontend/src/fileSender.js

@@ -1,5 +1,5 @@
 const EventEmitter = require('events');
-const { ivToStr, notify } = require('./utils');
+const { ivToStr } = require('./utils');
 
 class FileSender extends EventEmitter {
   constructor(file) {

frontend/src/utils.js

@@ -21,7 +21,7 @@ function strToIv(str) {
 }
 
 function notify(str) {
-  if (!("Notification" in window)) {
+  if (!('Notification' in window)) {
     return;
   } else if (Notification.permission === 'granted') {
     new Notification(str)