Haven’t use them, and can’t even remember are they there at all 
But have some deja vu… as if they ware in some other posts I have read searching for something else.
I have a custom module with some jQuery functions that calculate, disable, hide etc. some fields.
And it works great.
But I also have a wide range of user preferences, namely date formats.
I know that I can spit out a PHP value to JavaScript, but I wonder if they are already loaded and populated, so I can use them in my JS functions?
Any advise or guidance would be greatly appreciated!