Improve JavaScript

[malberts]

Blocks #67

Current JS CS review:

npm run grunt

The errors will cause CI failure, so this needs to be fixed first.

Also look at #76 (comment)

[malberts]

ESLint warning level for "no-jquery/no-class-state" must be removed as part of this task. The warning was added in #118 to make the current code at least pass CI.