Add eslint-plugin-compat.

We can check for browser compatibility on lint time now.

assets/js/src/pwa.js

@@ -5,14 +5,14 @@
 
   if ('serviceWorker' in navigator) {
     window.addEventListener('load', function () {
-      navigator.serviceWorker.register('/sw.js').then(function (registration) {
+      navigator.serviceWorker.register('/sw.js').then(function (registration) { // eslint-disable-line compat/compat
         console.log('ServiceWorker registration successful with scope: ', registration.scope)
         registration.onupdatefound = function () {
           var installingWorker = registration.installing
           installingWorker.onstatechange = function () {
             switch (installingWorker.state) {
               case 'installed':
-                if (navigator.serviceWorker.controller) {
+                if (navigator.serviceWorker.controller) { // eslint-disable-line compat/compat
                   console.log('new update available')
                   location.reload(true)
                 }

js/.eslintrc.json

@@ -7,6 +7,7 @@
     "jquery": true
   },
   "extends": "eslint:recommended",
+  "plugins": ["compat"],
   "parserOptions": {
     "ecmaVersion": 8,
     "sourceType": "module"
@@ -17,6 +18,7 @@
     "no-extra-parens": "error",
     "no-prototype-builtins": "error",
     "no-template-curly-in-string": "error",
+    "compat/compat": "error",
     "valid-jsdoc": "error",
 
     // Best Practices

package.json

@@ -85,6 +85,7 @@
     "clean-css-cli": "^4.1.6",
     "cross-env": "^5.0.5",
     "eslint": "^4.2.0",
+    "eslint-plugin-compat": "^1.0.4",
     "grunt": "^1.0.1",
     "grunt-cli": "^1.2.0",
     "grunt-saucelabs": "^9.0.0",