Using Post Thumbnails in a function

Hi everyone,

I was hoping someone could help me out. I’m learning javascript and wrote a script that changes the resolution size of a post thumbnail relative to the width of the browser but I am having trouble wrapping it in a function. I’m using the twenty eleven theme and it works fine wherever I cut and paste it but if I try to wrap it in a function the function call returns nothing. i’m assuming I’m doing everything wrong and that my in-line code is held together by fairy dust.

I need a good example of how to write a function that finds a posts post_thumbnail and returns the appropriate image in or out of the loop. Help or anything that could point me in the right direction would be greatly appreciated.

The concept:
I’m making a site with a fluid layout and my goal is to be able to resize my images to fit accordingly but at the same time be bandwidth wise. I don’t want to serve a 1500px wide image to a 320px wide phone. (Its an art portfolio site so its really image heavy.) For fixed images I can do this easily with css and media queries but for the embedded stuff I need a javascript solution. Post thumbnails seamed like a good way do this since they already generate several custom sizes. I’m by no means a coder but after a few late nights was able to get a proof of concept working, but it is by no means pretty and as i mentioned before only works in-line.

What is the proper way to do something like this?

Here is my humble little script: https://pastebin.com/RWWTqWJZ

thank you,

Ster