Checking if JS script exist on webpage

Hey Guys,
I want to create a ruby script to crawl a URL and check if a certain
script exists on the page.

I know I can crawl the URL with NOKOgiri or similar plugin. Would I be
able to check if the script exists without really firing the script.

use case - the JS script might or might not appear on certain pages of
the website. I want to check programmatically if that script is
available on the web page.

all help welcome, thnx guys