Can only add to that request. Do_I_miss the fade sound in/out function Flash had. 
I tried 'howler,js' but the examples out there go way too fast into "lets make this difficult" territory.
At least for me. 
""All"" I too, am looking for is a fade out action on a running sound when for example the current scene ends.
Fade in(s) I can create with 'Audacity'. Fade out(s) are sadly a lot more difficult to insert so the user experiences a nice, smooth transition in her/his eardrums.
Crappy thing is, I can, and do, look at supplied code here on the forum, it just remains largely 'abracadabra' for me. I'm unable to dissect the given code and distill the needed parts out of it to put it to my own use. Like this by @Daniel How to fade a sound, I just don't see how to use that, like how do I tell that snippet of code to apply to 'mySound'?