According to my expectations, after I read oficial docs, this method should serve all js from my collection as single string with code enclosed in <script> tags, however in my case it just returns empty string for non empty collection.
outputJs() for the same collection returns <script> tags with paths to included files in src attributes, in other words works as expected.
By the way, do I understand correctly that this Assets minification, regenerated every time? is still true?