I use "might" in these descriptions, because you will find they all cross over and are almost essentially the same package with a different odor.
UX Designers - might work more with wireframes, layouts etc. and is closer to a traditional graphic designer as they use a tool like photoshop or indesign to creak a mock up and send it to the Front-End developer to build.
Full stack JS - This sounds like either someone using a bunch of libraries (Angular with jQuery and some RequireJS or something like that). Otherwise, it might refer to MEAN developers (Mongo, Express, Angular, Node).
Web Design - that is so broad of a term, it could mean anything. Maybe someone who does both UX and Development, but is mainly developing 'Websites' not 'Web Apps'.
Front-end Web Dev - Mostly a HTML/CSS/JS wizard. Might have some UX skills, might also call themself a Web Designer, or Developer.
If you like using a language like Javascript, find out what you like about it and what you might use it for. Javascript can be used for more than just making a website look pretty and do fancy things. Chances are there will be someone asking you to do what they want (make it this color, make this disappear, draw this on a canvas etc.) and you just do it. At least learn HTML and CSS so you know how it relates to those.
Hope that helps.