Contoh DApp Dasar
Bangun DApp sederhana yang membaca data dari kontrak pintar yang telah diterapkan dan menampilkannya pada halaman web.
Contoh DApp Dasar adalah pelajaran Web3 & DApp Development Fundamentals gratis di CoddyKit. Ini adalah pelajaran 3 dari 3. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar Web3 & DApp Development Fundamentals, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus Web3 & DApp Development Fundamentals mencakup 3 pelajaran total.
Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.
Building Our First DApp
Welcome to building your first Decentralized Application (DApp)! In this lesson, we'll create a simple DApp that reads a message stored on a smart contract and displays it on a web page.
This example will tie together concepts you've learned about smart contracts and front-end interaction.
The Simple Message Contract
First, let's define the smart contract. This contract will be very basic: it just stores a single string variable, myMessage, which we'll make public so its value can be easily read from outside the contract.
Remember, this contract would be compiled and deployed to a blockchain (like Ethereum).
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
contract SimpleMessage {
string public myMessage = "Hello CoddyKit DApp!";
}Contract Address & ABI
Once our SimpleMessage contract is deployed to a blockchain, we get two critical pieces of information:
- Contract Address: This is like the contract's unique street address on the blockchain.
- ABI (Application Binary Interface): This is a JSON description of the contract's functions and variables. It tells our front-end how to 'talk' to the contract.
We'll use these in our web application to connect and read data.
Front-end HTML Structure
Our DApp needs a basic web page to display the message. We'll create an index.html file with a heading and a paragraph where our contract's message will appear. We'll also link our JavaScript file (app.js) and the Web3.js library.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>CoddyKit DApp</title>
</head>
<body>
<h1>DApp Message Reader</h1>
<p>Message from contract: <span id="contractMessage">Loading...</span></p>
<script src="https://cdn.jsdelivr.net/npm/web3@1.7.0/dist/web3.min.js"></script>
<script src="app.js"></script>
</body>
</html>Connecting with Web3.js
Now for the JavaScript (app.js)! We need to connect our web page to the Ethereum blockchain. The Web3.js library helps us do this. It will look for a provider, like MetaMask, in the user's browser.
// app.js
let web3;
async function initWeb3() {
if (window.ethereum) {
web3 = new Web3(window.ethereum);
try {
await window.ethereum.request({ method: 'eth_requestAccounts' });
console.log("Connected to MetaMask!");
} catch (error) {
console.error("User denied account access");
}
} else if (window.web3) {
web3 = new Web3(window.web3.currentProvider);
} else {
console.log('Non-Ethereum browser detected. Try MetaMask!');
// Fallback for read-only access (e.g., Infura)
// web3 = new Web3(new Web3.providers.HttpProvider("YOUR_INFURA_URL"));
}
}
Instantiating the Contract Object
With Web3.js connected to a provider, we can now create a JavaScript object that represents our deployed SimpleMessage smart contract. We do this using its contract address and ABI.
The ABI tells Web3.js which functions are available on the contract.
// app.js (continued)
const contractAddress = "0xYourDeployedContractAddressHere"; // REPLACE THIS!
const contractABI = [
{
"inputs": [],
"name": "myMessage",
"outputs": [
{
"internalType": "string",
"name": "",
"type": "string"
}
],
"stateMutability": "view",
"type": "function"
}
];
let simpleMessageContract;
async function loadContract() {
if (!web3) await initWeb3();
simpleMessageContract = new web3.eth.Contract(contractABI, contractAddress);
console.log("Contract loaded:", simpleMessageContract);
}Reading Contract Data
Now that we have our contract object, reading the myMessage variable is straightforward. Since myMessage is a public view variable, we can call its auto-generated getter function directly without sending a transaction (which means no gas cost).
// app.js (continued)
async function readMessage() {
if (!simpleMessageContract) await loadContract();
try {
// Call the auto-generated getter for 'myMessage'
const message = await simpleMessageContract.methods.myMessage().call();
console.log("Message from contract:", message);
return message;
} catch (error) {
console.error("Error reading message:", error);
return "Error loading message.";
}
}Full DApp JavaScript (app.js)
Here's the complete app.js file that ties everything together. It connects to the blockchain, loads the contract, reads the message, and then updates the HTML to display it when the page loads.
Remember to replace 0xYourDeployedContractAddressHere with your actual deployed contract address!
// app.js
let web3; // Declare web3 globally
const contractAddress = "0xYourDeployedContractAddressHere"; // REPLACE THIS!
const contractABI = [
{
"inputs": [],
"name": "myMessage",
"outputs": [
{
"internalType": "string",
"name": "",
"type": "string"
}
],
"stateMutability": "view",
"type": "function"
}
];
let simpleMessageContract;
async function initWeb3() {
if (window.ethereum) { web3 = new Web3(window.ethereum); await window.ethereum.request({ method: 'eth_requestAccounts' }); }
else if (window.web3) { web3 = new Web3(window.web3.currentProvider); }
else { console.log('Non-Ethereum browser detected. Try MetaMask!'); }
}
async function loadContract() {
if (!web3) await initWeb3();
simpleMessageContract = new web3.eth.Contract(contractABI, contractAddress);
}
async function readMessage() {
if (!simpleMessageContract) await loadContract();
try {
const message = await simpleMessageContract.methods.myMessage().call();
return message;
} catch (error) {
console.error("Error reading message:", error);
return "Error loading message.";
}
}
document.addEventListener('DOMContentLoaded', async () => {
const messageElement = document.getElementById('contractMessage');
await initWeb3();
await loadContract();
const msg = await readMessage();
messageElement.innerText = msg;
});DApp Interaction Check
Which of the following are essential pieces of information needed by a front-end DApp to interact with a deployed smart contract?
Recap: Your First DApp
Congratulations! You've just walked through the process of building a basic DApp.
- We defined a simple Solidity smart contract.
- We learned about the importance of the contract's address and ABI.
- We created an HTML page and used Web3.js to connect to the blockchain.
- Finally, we instantiated our contract object and read data from it, displaying it on our web page.
This fundamental pattern of connecting, interacting, and displaying is at the heart of most DApps!
Pertanyaan yang Sering Diajukan
Apakah pelajaran “Contoh DApp Dasar” gratis?
Ya — teks lengkap “Contoh DApp Dasar” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus Web3 & DApp Development Fundamentals, upgrade ke CoddyKit PRO. Kursus Web3 & DApp Development Fundamentals mencakup 3 pelajaran total.
Apa yang akan aku pelajari di “Contoh DApp Dasar”?
Bangun DApp sederhana yang membaca data dari kontrak pintar yang telah diterapkan dan menampilkannya pada halaman web. Kamu berlatih Web3 & DApp Development Fundamentals dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.
Apakah aku perlu pengalaman untuk memulai Web3 & DApp Development Fundamentals?
Tidak diperlukan pengalaman sebelumnya. Web3 & DApp Development Fundamentals di CoddyKit dirancang untuk pemula hingga pelajar tingkat lanjut, jadi kamu bisa memulai di sini atau dari awal dan belajar sesuai kecepatan kamu sendiri. Ini adalah pelajaran 3 dari 3.
Berapa lama pelajaran “Contoh DApp Dasar” memakan waktu?
Sebagian besar pelajaran CoddyKit memakan waktu sekitar 5–10 menit. Setiap pelajaran ringkas dan interaktif, jadi kamu membuat kemajuan stabil dan melanjutkan dari tempat kamu tinggalkan di web dan aplikasi.
Bisakah aku menulis dan menjalankan kode dalam pelajaran Web3 & DApp Development Fundamentals ini?
Ya. Setiap pelajaran Web3 & DApp Development Fundamentals menyertakan editor kode bawaan, jadi kamu menulis dan menjalankan kode nyata langsung di browser dan mendapatkan umpan balik AI instan — tidak diperlukan penyiapan lokal.