local-network-access

Chrome doesn't allow it - local network services have to opt-in to being fetchable from public sites (https://github.com/WICG/private-network-access), although they're replacing it with a user-permission-based approach (https://github.com/WICG/local-network-access). (There is some language online suggesting PNA has not actually shipped, but I experienced it myself in stable Chrome several years ago, so I am unsure of the current state). Firefox doesn't implement either approach -- I assume this is indicative of their lack of development resources.

There is a proposal to restrict sites from accessing a users' local network without permission: https://github.com/explainers-by-googlers/local-network-acce...