Add eslint no-undef rule and resolve errors

js/.eslintrc

@@ -2,7 +2,8 @@
     "root": true,
     "parser": "babel-eslint",
     "env": {
-        "browser": true
+        "browser": true,
+        "jquery": true
     },
     "rules": {
 
@@ -98,7 +99,7 @@
         "no-label-var": 2,
         "no-shadow": 0,
         "no-shadow-restricted-names": 2,
-        "no-undef": 0,
+        "no-undef": 2,
         "no-undefined": 0,
         "no-undef-init": 2,
         "no-unused-vars": 2,