Metamask: listen to solidity events with the supplier
When deploying an intelligent contract on Ethereum blockchain, it is common to use a supplier like Metamask to manage user interactions and events. In this article, we will explore how to listen to solidity events using the Metamask supplier.
What are solidity events?
Solide is a programming language used to write smart contracts on Ethereum blockchain. Solidity events are triggered by certain conditions or shares in a contract, such as when a function is performed or when a specific condition is fulfilled.
NODEJS with Websockets and Metamask
You have already successfully deployed your smart contract using Nodejs and a websocket supplier (WSS: //). This means that any user interacting with the contract may send transactions and receive events via the Ethereum network.
However, there are certain limits when it comes to listening to specific events on the contract. When you use Websockets with Metamask, you need to manually manage events on your Nodejs server side code.
The problem:
When a user interacts with your intelligent contract, the event is triggered and sent to the Ethereum network. But, since you run this code on your own machine (Nodejs), there is no direct way of receiving these events in real time.
This is where the Metamask supplier is useful. With Metamask, you can establish a connection with the blockchain contract using its public address and its private key.
Listen to solidity events with Metamask
Here is an example of how to listen to specific events on your contract using Metamask:
`Javascript
Const web3 = require ('web3');
Const MetamaskProvider = New Web3.Providers.httPProvider ('WSS: //your-compt-address.com');
// Get the contract body
Const contract = new web3.eth.contract (
"0xyourcontractaddress",
'0xyourcontractname'
));
// Define an event listening function
Onevent (eventtype, data) function {
Console.log (Event received: $ {eventtype} – $ {data});
}
// Create a new event of event earphones
Const Eventlisner = Contract.events [Eventype] .listen ((error, result) => {
if (error) {
launch an error;
}
Onevent (eventtype, result);
});
'
In this example:
- We create an instanceHTTPPROVIDER” with the public address and the private key to the contract.
- We get a reference to the contract body using its name or address.
- We define an event listening function which will be called each time an event is triggered.
- We use the `listening () ‘method of the contract body to subscribe to events. The recall function takes two arguments: “error” (if there is an error) and “result” (the event data).
- In the reminder, we call our listening function defined with the type of event and all the relevant event data.
How it works
Here is a step by step ventilation of the function of this code:
- You create an instance of the Web3 supplier using your contract address.
- You get a reference to the contract body using its name or address.
- You define an event listening function which will be called each time an event is triggered.
- When an event occurs, the contract sends it to the Ethereum network to the Metamask supplier.
- The Metamask supplier receives the event and transmits it to your code as an object with “error” and “result” properties.
- Your event listening function is called with the type of event and all the relevant data.
This approach allows you to listen to specific events on your contract using Metamask, without having to manually manage events on your code on the Nodejs server side.