Metamask: How can I use ether.js to listen for MetaMask events like `chainChained`?

Using Ethers.js to Listen to MetaMask Events

In recent years, the Ethereum ecosystem has seen significant adoption growth, leading to a surge in interest in using MetaMask, a popular browser extension for interacting with the Ethereum blockchain. When working with MetaMask, developers can use Ethers.js to receive real-time updates about account and chain changes.

Understanding MetaMask Events

MetaMask provides several events that allow users to interact with their accounts and the Ethereum network. Here’s a quick overview of some of the most commonly used events:

• accountsChanged: Fired when an account is updated, allowing you to update your local state in response.

• chainChanged: Fired when a user switches between different chains (e.g. from Mainnet to Testnet).

• blockNumber: Fired when a new block is mined on Ethereum.

Listening to MetaMask Events with Ethers.js

To listen to these events, you will need to use the window.ethereum object and create an event listener. Here is an example of how you can do this:

import * as ethers from ethers';
// Set up your provider and wallet
const provider = new ethers.providers.Web3Provider(window.ethereum);
const account = provider.getSigner();
// Define the events to listen for
const events = [
{ name: 'accountsChanged', callback: (account) => {
console.log(Account updated: ${account.address});
}},
{ name: 'chainChanged', callback: (newChainId) => {
console.log(Switching to chain ${newChainId}...);
}}
];
// Listen for events
provider.on('accountsChanged', (account) => events.find((e) => e.name === 'accountsChanged').callback(account));
provider.on('chainChanged', (newChainId) => events.find((e) => e.name === 'chainChanged').callback(newChainId));

import * as ethers from 'ethers';
// Set up your provider and wallet
const provider = new ethers.providers.Web3Provider(window.ethereum);
const account = provider.getSigner();
// Define events to listen for
const events = [
{ name: 'accountsChanged', callback: (account) => {
console.log(Account updated: ${account.address});
}},
{ name: 'chainChanged', callback: (newChainId) => {
console.log(Switching to chain ${newChainId}...);
}}
];
// Listen for events
provider.on('accountsChanged', (account) => events.find((e) => e.name === 'accountsChanged').callback(account));
provider.on('chainChanged', (newChainId) => events.find((e) => e.name === 'chainChanged').callback(newChainId));
// When an account or chain is updated, update the local state
function updateLocalState() {
const newAccount = account;
if (newAccount) {
console.log(Updating local state: ${newAccount.address});
}
}
// Add a callback to handle the update event
provider.on('accountsChanged', (account) => {
updateLocalState();
});
provider.on('chainChanged', (newChainId) => {
updateLocalState();
});

• Use window.ethereumas your provider and wallet.

• Define events that correspond to the MetaMask events you want to listen to (e.g.accountsChanged,chainChanged).

• Add event listeners to theaccountsChangedandchainChanged` events to ensure that updates are received from all affected chains.

By following these guidelines, you can effectively use Ethers.js to receive real-time updates about account and chain changes when working with MetaMask.