Is it possible to check which RPC APIs are available?

Question

Is it possible for a decentralized application to get details about the offered JSON-RPC APIs from the local ethereum node?

I want to check the following specs in the following order using web3.js:

1. Is the RPC port open and listening at :8545?
2. Is the RPC set to allow CORS requests from my domain (example.com)?
3. Which RPC APIs are availabe by the client (db,eth,net,web3)?

Is the 2nd step even possible if CORS is disabled for my remote domain? Will a disabled CORS RPC port be discoverable? If so, how?

Answer 1

1 and 2 can be checked with web3.isConnected()

3. You can only use web3 with web3.js

You can't check these if you don't have cors for your domain because you can't access the rpc without it