I'm curious about this too. And attempted this once and gave up, but maybe you can learn from what i tried. I ended up trying and failing was a UserScipt written in JS and that runs with a web browser add-on / extension. The UserScript did work for grabbing specific text elements off a website, but I had no way to store that data locally due to security limitations of web browsers. So it wasn't going to work for my needs.
Plan B which I have not tried yet but looked promising was with Python. There is a guide here i intended to follow but haven't yet :
https://realpython.com/beautiful-soup-web-scraper-python/