Listening to events on frontend in Blockchain / Solidity - Mini Project: Build & Apply

Listening to events on frontend

📖 Scenario: You are building a simple web page that listens to blockchain smart contract events and shows them live to users.This helps users see when something important happens on the blockchain, like a new token transfer.

🎯 Goal: Create a basic HTML page and JavaScript code that connects to a blockchain smart contract and listens to a specific event, then displays the event data on the page.

📋 What You'll Learn

Create an HTML page with a button to start listening to events

Add a JavaScript variable to hold the contract address

Use a JavaScript function to listen to the 'Transfer' event from the contract

Display the event details on the page when the event is received

💡 Why This Matters

🌍 Real World

Listening to blockchain events on the frontend helps users see live updates like token transfers or contract changes without refreshing the page.

💼 Career

Frontend developers working with blockchain need to handle smart contract events to build interactive and real-time user interfaces.

1

Create the HTML structure

Create a basic HTML page with a button element with id listenButton and a div element with id eventLog to show event messages.

Blockchain / Solidity

    
    
    Blockchain Event Listener


    

Need a hint?

Use a button with id listenButton and a div with id eventLog inside the body.

2

Add contract address variable

Add a JavaScript variable called contractAddress and set it to the string '0x1234567890abcdef1234567890abcdef12345678' inside a <script> tag before the closing </body> tag.

Blockchain / Solidity

    
    
    Blockchain Event Listener


    Start Listening
    
    
    // Your code here
    

Need a hint?

Use const contractAddress = '0x1234567890abcdef1234567890abcdef12345678'; inside a <script> tag.

3

Add event listening function

Inside the existing <script> tag, add a function called startListening that logs 'Listening to Transfer events...' to the console. Then add an event listener to the button with id listenButton that calls startListening when clicked.

Blockchain / Solidity

    
    
    Blockchain Event Listener


    Start Listening
    
    
    const contractAddress = '0x1234567890abcdef1234567890abcdef12345678';

    // Your code here
    

Need a hint?

Define startListening function that logs the message, then add a click event listener to the button.

4

Display event data on the page

Inside the startListening function, add code to append the text 'Transfer event received!' inside the div with id eventLog each time the function is called. Then test by clicking the button to see the message appear on the page.

Blockchain / Solidity

    
    
    Blockchain Event Listener


    Start Listening
    
    
    const contractAddress = '0x1234567890abcdef1234567890abcdef12345678';

    function startListening() {
        console.log('Listening to Transfer events...');
        // Your code here
    }

    document.getElementById('listenButton').addEventListener('click', startListening);
    

Need a hint?

Use document.getElementById('eventLog').textContent += 'Transfer event received!\n'; inside startListening.