Extending event emitters for Web3Provider

[trozler]

Hi,
Currently providers only provide support for a few events:
https://docs.ethers.io/v5/api/providers/provider/

However external provider (e.g. metamask) emit additional events that are useful when creating UIs.
https://docs.metamask.io/guide/ethereum-provider.html#events

For example:

ethereum.on('accountsChanged', (accounts) => {
  // Handle the new accounts, or lack thereof.
  // "accounts" will always be an array, but it can be empty.
});

ethereum.on('chainChanged', (chainId) => {
  // Handle the new chain.
  window.location.reload();
});

From eip-1193:
"
The Provider MUST implement the following event handling methods:
on
removeListener
"

In our case "The provider" would be the external provider defined.
Currently ethers.providers.ExternalProvider class does not support a .on() method.

It would be nice to have one of the following;
a) Expand events used in ethers.providers.Web3Provider class.
b) Allow events on ethers.providers.ExternalProvider.

Disclaimer:
I'm somewhat new to ethers and I do have the slight feeling that the above is by design. If yes, I would appreciate any guidance as to how I should be correctly handling these event using ethers.

Follow up:

I found and read the best practices section, where I can see you use the "network" event to detect network change. This is great and servers the same purpose as listening for "chainChanged".

      provider.on("network", (newNetwork, oldNetwork) => {
        // When a Provider makes its initial connection, it emits a "network"
        // event with a null oldNetwork along with the newNetwork. So, if the
        // oldNetwork exists, it represents a changing network
        if (oldNetwork) {
          window.location.reload();
        }
      });

Is there is a complete list of events that an ethers.providers.Web3Provider instance can listen for?
There is no mention of the network event in the docs.

Overall question
Should we be able to call provider.on(<events>) for the following events:

• accountsChanged
• chainChanged

As per EIP-1193.

Best,
Tony

[rolandsaven]

@trozler

Those events are EIP-1193 specific as you said. An ethers Provider is not related to an EIP-1193 compliant Provider as far as I'm concerned and according to what I've been reading on GitHub. It is just the name that confused me and probably you too.

An ethers Provider is a higher-level interface compared to an EIP-1193-compliant Provider. They don't necessarily have those events that are defined in the EIP-1193 standard. The ethers library creates a strong division between the operation a Provider can perform and those of a Signer, which for example Web3.js lumps together. A Provider in ethers is a read-only abstraction to access blockchain data.

See the common terminology in ethers' documentation.

I would recommend you the following issues and discussions to have a better understanding but again I'm not the owner of the project.

• The accountChanged event isn’t working on ethers Providers #1560
• Web3Provider not handling events, but window.ethereum object is #1396
• Support for Switching Chains with EIP-3326 #2842

I think what you can do is target the EIP-1193-compliant provider since an ethers provider wraps it. Note that provider.provider is probably only available in Web3Provider in some cases.

provider?.provider?.on("chainChanged", (chainId) => {
  // Handle the new chain
});