Ethereum: Capture emitted event with web3 v4.7.0

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Update to Ethereum Web3 v4.7.0: simple capture of outgoing events

As a developer building complex applications based on the Ethereum blockchain, one of the most challenging tasks we face is processing events coming from the network. In our case, we upgraded from version 1.x.x (the old version) to version 4.7.0 (our new favorite version), and now we really want to learn how to easily handle these generated events.

The first step in using Ethereum Web3 v4.7.0 is understanding the event generation process. In general, when an event is generated by a contract or a call to its function, it triggers a callback that is transmitted to all connected nodes in the network. This allows other applications and contracts to react to the event.

To intercept these events using our web3.js library (v4.7.0), we can use the on method provided by Web3.js. Here’s an example of how you can do it:

// Import the necessary modules

const Web3 = require('web3');

const web3 = new Web3();


// Get an instance of the Ethereum provider

const provider = new web3.providers.HttpProvider('


// Define a function for processing outgoing events

function onEvent(event) {

  // Check if this event is of interest (for example, "NewBlock")

  if (event.type === 'NewBlock') {

    console.log(New block received: ${event.data});

  }

}


// Subscribe to created events

web3.eth.on('block', onEvent);


// You can also specify a specific event type and callback function

web3.eth.on('TransactionHash', onEvent);

In this example, we import the Web3.js library and create an instance of the Ethereum provider. Then we define the on method, which listens for events of interest (in our case, “NewBlock”). The onEvent callback function is called whenever it receives an event broadcast to the network.

When you’re ready to disconnect from the network, simply call the off method on your instance:

web3.eth.off('block', onEvent);

By following this example and using Web3.js v4.7.0, we can easily capture generated events in our applications and react accordingly.

Tips and Options

• Be sure to replace ” with your actual Infura project ID.

• You can also specify a callback function or event handler as an argument to the on method, for example: web3.eth.on('NewBlock', onEvent).

• Keep in mind that events are created only when the contract is called. For example, if you call a contract function from a second contract, it will not generate an event.

• If you need more control over event processing (for example, for complex use cases), consider using Web3.js v5.x.x.

We hope this helps! Let us know in the comments if you have any questions or need additional help.

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