How to check if a user has a certain extension installed?

Question

JavaScript

Here I have a site and I need to find out if the user has the extension installed knowing his key or in some other way? the extension is not mine, for example, I can give an extension for ip substitution, so I need to find out if the user has it installed

Answer 1

See what extension. AdBlock, for example, is detected quite successfully by indirect signs.
In most cases, of course, this cannot be determined, but in some it is possible.
You need to know very well the specifics of the extension and what exactly it does with the page.