Related: This is a nice write-up of how to write reactive jQuery. It's presented as an alternative to jQuery spaghetti code, in the context of being in a legacy codebase where you might not have access to newer frameworks. https://css-tricks.com/reactive-jquery-for-spaghetti-fied-le...
I used this approach before and it indeed works better than the 2010-style jQuery mess. A good fit for userscripts too, where the problem you attempt to solve is fairly limited and having dependencies, especially with a build steps, is a pain. Note that you don't need jQuery for this at all, unless you are somehow stuck with ancient browser support as a requirement - querySelector, addEventListener, innerHtml - the basic building blocks of the approach - have been available and stable for a long time.