Metamask: It is possible to listen Solidity events with Metamask provider?

Metamask: Listening to Solidity Events with the 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 explore how to listen to Solidity events using the Metamask provider.

What are Solidity events?

Solidity is a programming language used for writing smart contracts on the Ethereum blockchain. Events in Solidity are triggered by certain conditions or actions within a contract, such as when a function is executed or when a certain condition is met.

NodeJS with WebSockets and MetaMask

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

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

Problem:

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

That is where the Metamask provider comes in handy. With MetaMask, you can establish a connection to the 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-contract-address.com');
// Get the contract instance
const contract = new web3.eth.Contract(
"0xYourContractAddress",
"0xYourContractName"
);
// Define an event listener function
function onEvent(eventType, data) {
console.log(Event received: ${eventType} - ${date});
}
// Create a new event listener instance
const eventListener = contract.events[eventType].listen((error, result) => {
if (error) {
throw error;
}
onEvent(eventType, result);
});

In this example:

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

• We get a reference to the contract instance using 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 there is an error) and result (the event data).

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

How ​​it works

Here is a step-by-step breakdown of how this code works:

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

• Get a reference to the contract instance using its name or address.

• 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 passes it back to your code as an object with properties “error” and “result”.

• Your event listener function is called with the event type and any relevant data.

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