Yep, a dark corner of the JS, which can be confusing and misleading
How browsers schedule and execute scripts can impact the performance of web pages. While techniques like
<link rel=preload>(and others) influence script loading, knowing how browsers interpret them can also be helpful. Thanks to Kouhei Ueno, we now have an up to date summary of script scheduling in Chrome.
Even more details in Scheduling Scripts Intuitively and Performantly (google doc presentation)
and a nice summary in image