How to make a simple browser extension/custom js?

Question

JavaScript

It is necessary to make an extension to the browser, which, after loading the page of a certain site, finds a certain element in the dom (it may not arrive in the html source, but be formed on the browser side), takes text from it, sends a request with this text to an external service and displays a response service to another dom element.

There is no experience with front-end development, even less with browser extensions), but I will somehow figure it out with writing the logic of the code itself. But how to implement it (namely, an extension? a loadable script? something else?) and how to ensure its call at the right time is completely incomprehensible.

I would be very grateful for a link to articles with similar examples analyzed.
Browser, extension type, protocol for interacting with an external service will suit anyone.

Answer 1

The development of an extension is sometimes a hemorrhagic topic.
But in essence, you will be developing an HTML + CSS + JS application. Like a site. But with some peculiarities.
You can start, for example, with this . And all the steps left and right to google.