[Capturing knob position after user has interacted]

I'm thinking that although my application is not a game, just a sorting mechanism, that what I'm trying to do is a normal kind of functionality in a javascript html5 game... I'll start looking at resources for that, but if anyone has any advice for me to learn this I'd appreciate it.

[Capturing knob position after user has interacted]

I've little experience with HTML5 and Javascript. I've only built sites with templates, and I'm attempting my first project that really requires a site built from scratch. I want to use knobs to sort images based on the knob setting, so I've got the draggable knob up and running, now I'm wondering how to even search this forum for answers on how to capture the knob's new position as a variable I can use to sort some images. 

 

I've got some examples of image sorts by tab pushes, so what I'd like to do is capture the knob's position after the user rotates it, set a variable and when the user presses sort, insert the variable value to duplicate the effect of a tab push.

 

I'd appreciate any links to tutorials or documentation I can read that is specifically about this kind of task. 

 

Best, Marc