They're reasonable signs that the JavaScript is non-trivial, not restrictions. You can write a program that uses them and release it under a free software license and LibreJS will run it.
Here's a good example of a trivial JavaScript program.
For any non-trivial JavaScript programs, a free software license is required if you want it to be run by LibreJS -- a program designed to block any nonfree software from running on your computer inside a web browser.
I don't understand this view point. If this is about Free Software, then triviality should be irrelevant, either the code is Free or it isn't. I can write an arbitrarily complicated program within their constraints, license it under a non-free license and this thing will run it.
Here's a good example of a trivial JavaScript program.
<a href="#" onclick="javascript:alert('hello world')">click me</a>
For any non-trivial JavaScript programs, a free software license is required if you want it to be run by LibreJS -- a program designed to block any nonfree software from running on your computer inside a web browser.