Building a Decentralized Voting Application with QuickNode and Solidity
Tags: solidity, blockchain, webdev, programming
Published: 2023-06-20 19:34:20

## Introduction
In this tutorial, we will explore how to build a decentralized voting application using QuickNode as our Ethereum provider and Solidity as the smart contract programming language. Decentralized voting systems offer transparency, immutability, and security, making them ideal for various use cases. Let's get started!

## Prerequisites
- Basic understanding of Ethereum blockchain and smart contracts
- Familiarity with Solidity programming language
- QuickNode Ethereum account and API key

## Step 1: Setting Up the Development Environment
- Install and configure the required tools: Node.js, npm, and a code editor.
- Create a new directory for your project and initialize a new npm project.
- Install necessary dependencies such as web3.js and truffle.

```
mkdir decentralized-voting
cd decentralized-voting
npm init -y
npm install web3 truffle
```

## Step 2: Designing the Smart Contract
- Define the structure of the voting contract, including state variables, constructor, and relevant functions.
- Implement functions for adding candidates, casting votes, and retrieving voting results.
- Compile the smart contract using the Solidity compiler.

**Create a new file called `Voting.sol` and add the following code:**

```
pragma solidity ^0.8.0;

contract Voting {
    mapping(string => uint256) public votes;
    string[] public candidates;

    constructor(string[] memory _candidates) {
        candidates = _candidates;
    }

    function addCandidate(string memory candidate) public {
        candidates.push(candidate);
    }

    function vote(uint256 candidateIndex) public {
        require(candidateIndex < candidates.length, "Invalid candidate index");
        votes[candidates[candidateIndex]]++;
    }

    function getVotes(string memory candidate) public view returns (uint256) {
        return votes[candidate];
    }
}

```

## Step 3: Deploying the Smart Contract
- Configure your QuickNode Ethereum provider in your development environment.
- Create a migration script using Truffle to deploy the smart contract to the Ethereum network.
- Deploy the contract using Truffle's deployment commands.

**Create a new file called `2_deploy_contracts.js` in the `migrations` directory and add the following code**

```
const Voting = artifacts.require("Voting");

module.exports = function (deployer) {
  const candidates = ["Candidate 1", "Candidate 2", "Candidate 3"];
  deployer.deploy(Voting, candidates);
};

```

## Step 4: Building the User Interface
- Create a simple HTML file to display the voting interface.
- Connect the user interface to the deployed smart contract using web3.js.
- Implement functions to interact with the smart contract, such as adding candidates, casting votes, and retrieving results.

**Create a new HTML file called `index.html` and add the following code**

```
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Decentralized Voting Application</title>
</head>
<body>
    <h1>Decentralized Voting Application</h1>
    
    <h2>Candidates:</h2>
    <ul id="candidates-list"></ul>
    
    <h2>Vote</h2>
    <select id="candidate-select"></select>
    <button id="vote-button">Vote</button>
    
    <h2>Results:</h2>
    <ul id="results-list"></ul>

    <script src="./app.js"></script>
</body>
</html>
```
**Create a new JavaScript file called `app.js` and add the following code**

```
const contractAddress = "YOUR_CONTRACT_ADDRESS"; // Update with the deployed contract address
const abi = [/* Add the ABI of the deployed contract here */];

const web3 = new Web3("https://quicknode.com/rpc/your-quicknode-api-key"); // Update with your QuickNode API key

const votingContract = new web3.eth.Contract(abi, contractAddress);

async function initialize() {
    const candidatesList = document.getElementById("candidates-list");
    const candidateSelect = document.getElementById("candidate-select");
    const resultsList = document.getElementById("results-list");

    const candidatesCount = await votingContract.methods.candidates.length().call();
    for (let i = 0; i < candidatesCount; i++) {
        const candidate = await votingContract.methods.candidates(i).call();
        candidatesList.innerHTML += `<li>${candidate}</li>`;
        candidateSelect.innerHTML += `<option value="${i}">${candidate}</option>`;
    }

    const voteButton = document.getElementById("vote-button");
    voteButton.addEventListener("click", async () => {
        const selectedCandidateIndex = candidateSelect.value;
        await votingContract.methods.vote(selectedCandidateIndex).send({ from: web3.eth.defaultAccount });
        alert("Vote cast successfully!");
        updateResults();
    });

    async function updateResults() {
        resultsList.innerHTML = "";
        for (let i = 0; i < candidatesCount; i++) {
            const candidate = await votingContract.methods.candidates(i).call();
            const votes = await votingContract.methods.getVotes(candidate).call();
            resultsList.innerHTML += `<li>${candidate}: ${votes} votes</li>`;
        }
    }

    updateResults();
}

window.addEventListener("load", async () => {
    // Load the user's Ethereum account
    const accounts = await web3.eth.getAccounts();
    web3.eth.defaultAccount = accounts[0];

    initialize();
});
```

> [Why Businesses Choose QuickNode for Web3 Infrastructure](https://blog.quicknode.com/why-businesses-choose-quicknode-for-web3-infrastructure/)

## Step 5: Testing the Application
- Run the local development server and open the voting application in a web browser.
- Perform various actions, such as adding candidates, casting votes, and checking voting results.
- Verify that the application functions as expected and the smart contract updates accordingly.

**To start the local development server, run the following command**

```
npm run dev
```
Open your web browser and navigate to `http://localhost:3000` to access the decentralized voting application.

## Step 6: Deploying the Application
- Build the production-ready version of the application using npm scripts.
- Host the application on a static web hosting platform, such as GitHub Pages or Netlify.
- Verify that the deployed application interacts correctly with the Ethereum network.

## Conclusion
Congratulations! You have successfully built a decentralized voting application using QuickNode as the Ethereum provider and Solidity for smart contract development. By leveraging the power of QuickNode's infrastructure and the transparency of blockchain technology, you have created a secure and tamper-proof voting system. Feel free to enhance and customize the application further to suit your specific requirements.

Remember to follow best practices for security and thoroughly test your application before deploying it to the production environment.

Happy coding and exploring the world of decentralized applications with QuickNode and Solidity!