Drupal JavaScript leaves a lot to be desired. There is a bit of unoptimized code. Most of the JS is uncompressed. We load a lot of JS in the head that would be more performant to load in the footer. There are a number of anit-patterns in the JS. I could go on and on.
For Drupal 8 and moving forward we need a game plan for our JavaScript. This BoF would be a start to get us coordinated and moving in a better direction.
See also
See also #784626.