Metamask: Is it possible to listen Solidity events with Metamask provider?

Metamask: Listening to Solidity Events Using a Provider

When implementing a smart contract on the Ethereum blockchain, it is common to use a provider like MetaMask to handle user interactions and events. In this article, we will see how to listen to Solidity events using the Metamask provider.

What are Solidity Events?

Solidity is a programming language used to write smart contracts on the Ethereum blockchain. Events in Solidity are triggered by certain conditions or actions within a contract, such as the execution of a function or the satisfaction of a certain condition.

NodeJS with WebSockets and MetaMask

You have now successfully deployed your smart contract using NodeJS and the WebSocket provider (wss://). This means that any user interacting with the contract will be able to send transactions and receive events over the Ethereum network.

There are some limitations when it comes to listening to specific events in a contract, however. When using WebSockets with MetaMask, you have to manually handle the events in your server-side NodeJS code.

Problem:

When a user interacts with your smart contract, an event is triggered and sent to the Ethereum network. However, since you are running this code on your computer (NodeJS), there is no direct way to receive these events in real-time.

This is where the Metamask provider comes in handy. With MetaMask, you can connect to a contract on the blockchain using its public address and private key.

Listening to Solidity Events with Metamask

Here is an example of how you can listen to specific events in your contract using Metamask:

const Web3 = require('web3');
const metamaskProvider = new Web3.providers.HttpProvider('wss://your-contractual-address.com');
// Get the contract instance
const contract = new web3.eth.Contract(
'0xYourContractualAddress',
"0xYourContractName"
);
// Set the event listener function
function onEvent(eventType, data) {
console.log(Event received: ${eventType} - ${data});
}
// Create a new event listener instance
const eventListener = contract.events[eventType].listen((error, result) => {
if (error) {
throw an error;
}
onEvent(eventType, result);
});

In this example:

• We create an HttpProvider instance with the public contract address and private key.

• We get a reference to a contract instance by its name or address.

• We define an event listener function that will be called whenever an event is triggered.

• We use the listen() method of the contract instance to subscribe to events. The callback function takes two arguments: error (if an error occurs) and result (the event data).

• In the callback, we call our defined event listener function with the event type and all relevant event data.

How ​​it works

Here is a detailed description of how this code works:

• You create an instance of the Web3 provider using your contract address.

• You receive a reference to a contract instance using its name or address.

• You define an event listener function that will be called whenever an event is triggered.

• When an event occurs, the contract sends it over the Ethereum network to the MetaMask provider.

• The MetaMask provider receives the event and returns it to the code as an object with the properties “error” and “result”.

• The event listener function is called with the event type and all relevant data.

This approach allows you to listen for specific events in a contract using Metamask, without having to manually handle events in the server-side NodeJS code.