Day30: Real-World Blockchain (7) – Using and Interacting with Smart Contracts

·

Smart contracts are the backbone of decentralized applications (dApps) on blockchain platforms like Ethereum. They enable trustless, automated execution of agreements without intermediaries. In this article, we’ll explore how smart contracts are used in real-world applications, how users interact with them through web interfaces, and the tools and concepts essential for seamless integration—such as ABI, Web3.js, and MetaMask.

Whether you're a developer building your first dApp or a curious user trying to understand what happens behind the scenes when you click “Confirm” in a wallet, this guide breaks down the mechanics in a clear, practical way.

How Smart Contracts Are Triggered

Interacting with a smart contract is similar to sending a standard cryptocurrency transaction—but with added data. When a user wants to execute a function within a smart contract, they send a transaction to the contract’s address. Unlike regular ETH transfers, this transaction includes input data that specifies which function to call and what parameters to pass.

For example, if a contract has a transfer(address to, uint256 amount) function, the input data encodes both the function signature (transfer) and the arguments (recipient address and amount). Miners include this transaction in a block, and upon confirmation, the Ethereum Virtual Machine (EVM) executes the specified function.

Notably, these transactions don’t always involve sending ETH. However, if the function is marked as payable, users can include ETH as part of the transaction.

👉 Discover how blockchain transactions power smart contract interactions today.

Understanding Application Binary Interface (ABI)

To interact with a smart contract, you need to know its structure: what functions it exposes, their parameters, return types, and whether they modify blockchain state. This is where the Application Binary Interface (ABI) comes in.

Think of the ABI as a contract’s public instruction manual. It’s a JSON-formatted definition that describes every callable function and event in the contract. Without it, external applications wouldn’t know how to format their calls correctly.

Here’s an excerpt of what an ABI entry looks like:

{
  "type": "function",
  "name": "transfer",
  "inputs": [
    { "name": "to", "type": "address" },
    { "name": "amount", "type": "uint256" }
  ],
  "outputs": [],
  "stateMutability": "nonpayable"
}

Key ABI Properties:

It's important to note: once deployed, a smart contract’s bytecode cannot be reverse-engineered to retrieve its original source code or ABI. Platforms like Etherscan display verified contract ABIs only because developers voluntarily submit their source code for verification.

This transparency builds trust—users can audit the logic before interacting.

Connecting Web Applications with Ethereum

One major barrier to mainstream blockchain adoption is usability. Unlike traditional apps that rely on usernames and passwords, blockchain interactions require cryptographic wallets. So how do websites bridge this gap?

The solution lies in integrating wallet connectivity directly into web pages—enabling users to sign transactions securely without leaving the browser.

Introducing MetaMask: Your Gateway to dApps

MetaMask is the most widely used browser extension wallet for Ethereum and EVM-compatible chains. It acts as an intermediary between your web browser and the Ethereum network.

Once installed (typically as a Chrome extension), MetaMask injects a window.ethereum object into web pages. This allows websites to detect if a user has a wallet and request permissions to read account data or send transactions.

With MetaMask, users retain full control over their private keys while enjoying seamless interaction with dApps—making it foundational for modern decentralized experiences.

👉 Learn how to integrate secure wallet access into your next blockchain project.

Web3.js: The Bridge Between Frontend and Blockchain

While MetaMask handles identity and signing, Web3.js enables actual communication with the Ethereum blockchain. It’s a JavaScript library that lets frontends query blockchain data and send transactions using familiar syntax.

Developers embed Web3.js in their web apps to perform actions like checking balances, reading contract data, or triggering state changes—all through simple API calls.

Setting Up Web3.js

To connect to Ethereum, Web3.js needs access to a node. Since running your own node is resource-intensive, most developers use services like Infura or Alchemy to get reliable API endpoints.

const Web3 = require('web3');
let web3;

if (window.ethereum) {
  web3 = new Web3(window.ethereum);
  await window.ethereum.enable(); // Request user permission
} else {
  web3 = new Web3(new Web3.providers.HttpProvider('https://mainnet.infura.io/v3/YOUR_API_KEY'));
}

Common Web3.js Operations

Get Account Balance

const balance = await web3.eth.getBalance('0x...');
const ethBalance = web3.utils.fromWei(balance, 'ether');
console.log(`${ethBalance} ETH`);

Send ETH

const tx = {
  from: '0xSender',
  to: '0xRecipient',
  value: web3.utils.toWei('0.1', 'ether'),
  gas: 21000
};

await web3.eth.sendTransaction(tx);

Interact With Smart Contracts

First, instantiate the contract using its ABI and address:

const contract = new web3.eth.Contract(abi, '0xContractAddress');

Then use .call() for read-only operations (free) or .send() for state-changing ones (gas required):

// Read data (no cost)
contract.methods.balanceOf('0xUser').call()
  .then(console.log);

// Write data (requires gas)
contract.methods.transfer('0xTo', '100')
  .send({ from: '0xFrom' })
  .on('transactionHash', hash => console.log(hash));

Core Keywords for SEO & Search Intent

This article targets users interested in practical blockchain development. Key terms naturally integrated include:

These reflect high-intent queries from developers and learners seeking hands-on knowledge.

Frequently Asked Questions (FAQ)

Q: Can I interact with smart contracts without coding?

Yes! Many dApps like Uniswap or Aave provide user-friendly interfaces where you can swap tokens or lend assets without writing code. Under the hood, they use Web3.js and MetaMask just like described here.

Q: Is ABI required every time I interact with a contract?

Yes. The ABI tells your application how to encode function calls properly. If you're using tools like Etherscan or Remix, they often fetch verified ABIs automatically.

Q: What happens if I send a transaction with incorrect input data?

The transaction may fail and still consume gas because miners processed it. Always test on testnets first using tools like Ganache or Sepolia.

Q: Can I modify a deployed smart contract?

Generally no—blockchain immutability means contracts can't be altered after deployment. However, advanced patterns like proxy contracts allow upgradeable logic while preserving data.

Q: Why do some functions cost gas while others don’t?

Functions that only read data (view, pure) don’t change blockchain state and thus cost nothing. Functions that write or modify data require miners to validate changes, so they incur gas fees.

Q: How do I find a contract’s ABI?

You can retrieve it from Etherscan if the contract is verified. Alternatively, developers usually publish ABIs in their GitHub repositories or documentation.

👉 Start building your own dApp with trusted tools and resources now.

Final Thoughts: Building Real-World Blockchain Fluency

Understanding how smart contracts work—from triggering functions to decoding ABI and using Web3.js—is essential for anyone entering blockchain development. While the learning curve is steep, tools like MetaMask and Infura have dramatically lowered entry barriers.

As blockchain continues evolving, fluency in these core concepts will remain vital—not just for developers, but for informed users navigating decentralized ecosystems.

Whether you're completing a learning challenge or launching your first dApp, remember: consistent practice, structured planning, and leveraging community resources make all the difference.