0Pricing
Web3 & DApp Development Fundamentals · Lesson

Handling Transactions & Events

Learn to send transactions from your DApp, handle transaction confirmations, and listen for smart contract events to update the UI.

Handling Transactions & Events is a free Web3 & DApp Development Fundamentals lesson on CoddyKit — lesson 3 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Web3 & DApp Development Fundamentals learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Making DApps Dynamic

So far, you've learned how to connect your DApp to the blockchain and read data. But what if you want to change data or perform actions?

This lesson teaches you how to send transactions from your DApp to modify blockchain state and how to listen for real-time updates using smart contract events.

What is a Blockchain Transaction?

A blockchain transaction is a signed message that changes the state of the blockchain. Every transaction costs a small fee called gas, paid in Ether (ETH).

Common DApp transactions include:

  • Sending Ether to another address.
  • Calling a smart contract function that writes or modifies data.
  • Deploying a new smart contract.

Sending Transactions from Your DApp

To send a transaction that calls a smart contract function, your DApp needs to:

  1. Connect to a blockchain provider (e.g., MetaMask).
  2. Get a signer (the connected user's wallet).
  3. Call the desired contract function, passing any required parameters.

The user's wallet will then prompt them to confirm and sign the transaction.

Calling a Write Function Example

Here's how you might call a simple setValue function on a smart contract using Ethers.js. Remember, contract refers to your instantiated contract object.

// Assuming 'contract' is an Ethers.js Contract instance
// and 'signer' is obtained from the connected wallet.

async function updateValue(newValue) {
  try {
    const tx = await contract.connect(signer).setValue(newValue);
    console.log("Transaction sent: ", tx.hash);
    // Wait for the transaction to be mined
    await tx.wait();
    console.log("Transaction confirmed!");
  } catch (error) {
    console.error("Error sending transaction:", error);
  }
}

Waiting for Transaction Confirmation

After sending a transaction, it's not immediately processed. It goes into a transaction pool and waits to be included in a block by a miner or validator.

The await tx.wait() call is crucial. It pauses your DApp's execution until the transaction is mined and confirmed on the blockchain, ensuring your UI reflects the latest state.

Understanding Transaction Receipts

When tx.wait() resolves, it returns a transaction receipt. This receipt contains important information about the transaction's outcome:

  • blockHash and blockNumber: Where it was included.
  • gasUsed: The actual gas consumed.
  • status: Indicates if the transaction was successful (1) or failed (0).

Always check the status to ensure the contract call executed as expected!

Introducing Smart Contract Events

Smart contract events are a powerful mechanism for your contracts to 'broadcast' information to external applications (like your DApp) when something significant happens.

Think of them as logs or notifications that DApps can listen to. They are a cost-effective way to communicate data from the blockchain without storing it directly on-chain.

Emitting Events in Solidity

In Solidity, you first define an event with its parameters, then use the emit keyword to trigger it within a function. Here's a simple example:

pragma solidity ^0.8.0;

contract MyContract {
  uint public value;

  // Define an event
  event ValueChanged(address indexed user, uint oldValue, uint newValue);

  function setValue(uint _newValue) public {
    uint _oldValue = value;
    value = _newValue;
    // Emit the event
    emit ValueChanged(msg.sender, _oldValue, _newValue);
  }
}

Listening for Events in Your DApp

Your DApp can subscribe to specific events emitted by a contract. When an event occurs, your DApp receives the event data, allowing you to update the UI or trigger other actions in real-time.

This avoids constant 'polling' (repeatedly asking the blockchain for updates), making your DApp more efficient.

// Assuming 'contract' is an Ethers.js Contract instance

contract.on("ValueChanged", (user, oldValue, newValue, event) => {
  console.log(`Value changed by ${user}`);
  console.log(`From ${oldValue} to ${newValue}`);
  // Update your DApp's UI here, e.g., display the new value
  updateDisplay(newValue);
});

console.log("Listening for ValueChanged events...");

Quick Check: Tx & Events

When calling a smart contract function that modifies state from your DApp, what is the primary purpose of using await tx.wait()?

Recap & Next Steps

You've learned how to make your DApps truly interactive!

  • You can now send transactions to modify blockchain state.
  • You know how to wait for confirmation and handle transaction receipts.
  • You understand how smart contract events provide real-time updates to your DApp.

These skills are fundamental for building dynamic and responsive decentralized applications. Keep practicing to master DApp interaction!

Frequently asked questions

Is the “Handling Transactions & Events” lesson free?

Yes — the full text of “Handling Transactions & Events” is free to read here on the web, and the Web3 & DApp Development Fundamentals course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Web3 & DApp Development Fundamentals course, upgrade to CoddyKit PRO.

What will I learn in “Handling Transactions & Events”?

Learn to send transactions from your DApp, handle transaction confirmations, and listen for smart contract events to update the UI. You practise Web3 & DApp Development Fundamentals with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Web3 & DApp Development Fundamentals?

No prior experience is required. Web3 & DApp Development Fundamentals on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 3, so you can start here or from the beginning and move at your own pace.

How long does the “Handling Transactions & Events” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Web3 & DApp Development Fundamentals lesson?

Yes. Every Web3 & DApp Development Fundamentals lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. React & Web3 Frameworks
  2. Integrating Wallets
  3. Handling Transactions & Events
← Back to Web3 & DApp Development Fundamentals