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Providers Events Listening

Some providers are, by design, always connected. Therefor, they can communicate changes with the user through events. Actually, among the 3 providers, HttpProvider is the only one that does not support event. And the other 2: WebSocketProvider and IpcProvider enable the user to listen to emitted events.

Actually, the events can be categorized as follows (according to EIP 1193):

  • Communicate arbitrary messages: message
  • Changes to the Provider’s ability to make RPC requests;
    • connect
    • disconnect
  • Common Client and/or Wallet state changes that any non-trivial application must handle:
    • chainChanged
    • accountsChanged

Below a sample code for listening and remove listening to EIP 1193 events:

Listening to EIP1193 events
import { Web3 } from 'web3';

const web3 = new Web3(/* PROVIDER*/);

web3.provider.on('message', () => {
  // ...
});

web3.provider.on('connect', () => {
  // ...
});

web3.provider.on('disconnect', () => {
  // ...
});

web3.provider.on('accountsChanged', () => {
  // ...
});

web3.provider.on('chainChanged', () => {
  // ...
});

// it is possible to catch errors that could happen in the underlying connection Socket with the `error` event
// and it is also used to catch the error when max reconnection attempts is exceeded
//  as in section: /docs/guides/web3_providers_guide/#error-message
web3.provider.on('error', () => {
  // ...
});

// ...

// for every event above `once` can be used to register to the event only once
web3.provider.once('SUPPORTED_EVENT_NAME', () => {
  // ...
});

// And to unregister a listener `removeListener` could be called
web3.provider.removeListener('SUPPORTED_EVENT_NAME', () => {
  // ...
});

However, the underlying SocketConnection of both WebSocketProvider and IpcProvider could be accessed. This enables the user to access any special properties of the used Socket. As well as, registering to the custom server events directly. Actually the Socket used at WebSocketProvider is isomorphic-ws. And the Socket used at IpcProvider is net.Server