web3-crowdfund

FundChain — Decentralized Crowdfunding dApp

Trustless crowdfunding on Ethereum. Create campaigns, contribute ETH, and withdraw only when goals are met — all enforced by smart contract.

Live Demo: parth1305.github.io/web3-crowdfund
Contract: 0x189ab20b1993166d1c498c5acafa396658d2fea5 on Sepolia

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Overview

FundChain is a full-stack Web3 application that demonstrates end-to-end blockchain development — from a Solidity smart contract deployed on Ethereum Sepolia, to a Node.js/Express backend API, to a vanilla JS frontend.

No intermediaries. No trust required. The contract enforces all rules.

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How It Works

1. Create a campaign — set a title, ETH goal, and deadline
2. Contribute ETH — anyone can send ETH to an active campaign
3. Withdraw — owner can withdraw only if the goal is met before the deadline
4. Refund — contributors can claim refunds if the goal wasn’t met

All logic lives on-chain. The backend is a read/write API layer over the contract.

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Tech Stack

Layer	Technology
Smart Contract	Solidity 0.8.28, Hardhat v3
Blockchain	Ethereum Sepolia Testnet
Backend	Node.js, Express, TypeScript, viem
Frontend	Vanilla HTML/CSS/JS
RPC	Alchemy
Deploy	GitHub Pages (frontend)

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Project Structure

web3-crowdfund/
├── contracts/
│   └── Crowdfund.sol          # Solidity smart contract
├── test/
│   └── Crowdfund.test.ts      # 9 passing tests
├── scripts/
│   └── deploy.ts              # Hardhat deploy script
├── backend/
│   └── src/
│       ├── index.ts           # Express server (port 3001)
│       ├── contract.ts        # viem client + ABI
│       └── routes.ts          # API route handlers
├── frontend/
│   └── index.html             # Single-page frontend
└── hardhat.config.ts

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Smart Contract

contracts/Crowdfund.sol

struct Campaign {
    address owner;
    string title;
    uint256 goal;
    uint256 deadline;
    uint256 amountRaised;
    bool withdrawn;
}

Functions:

• createCampaign(title, goal, durationInDays) — creates a new campaign
• contribute(campaignId) — send ETH to a campaign (payable)
• withdraw(campaignId) — owner withdraws if goal met
• refund(campaignId) — contributor claims refund if goal not met
• getCampaign(campaignId) — read campaign data

Security: Reentrancy protection via state updates before external calls.

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API Endpoints

Method	Endpoint	Description
GET	/api/campaigns	List all campaigns
GET	/api/campaigns/:id	Get single campaign
POST	/api/campaigns	Create new campaign
POST	/api/campaigns/:id/contribute	Contribute ETH

Example — Create Campaign:

curl -X POST http://localhost:3001/api/campaigns \
  -H "Content-Type: application/json" \
  -d '{"title": "My Campaign", "goalInEth": "0.05", "durationInDays": 30}'

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Running Locally

Prerequisites

• Node.js v18+
• An Alchemy account (free tier works)
• A funded Sepolia wallet

1. Clone the repo

git clone https://github.com/Parth1305/web3-crowdfund.git
cd web3-crowdfund

2. Install dependencies

npm install
cd backend && npm install && cd ..

3. Set environment variables

export SEPOLIA_RPC_URL="https://eth-sepolia.g.alchemy.com/v2/YOUR_KEY"
export SEPOLIA_PRIVATE_KEY="0xYOUR_PRIVATE_KEY"
export CROWDFUND_CONTRACT_ADDRESS="0x189ab20b1993166d1c498c5acafa396658d2fea5"

4. Run tests

npx hardhat test
# 9 passing

5. Start the backend

cd backend
npm run dev
# Server running on http://localhost:3001

6. Open the frontend

Open frontend/index.html in your browser.

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Deploying the Contract

npx hardhat run scripts/deploy.ts --network sepolia

Update CROWDFUND_CONTRACT_ADDRESS and the address in frontend/index.html with the new contract address.

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Tests

✓ should create a campaign
✓ should allow contributions
✓ should allow owner to withdraw when goal is met
✓ should prevent withdrawal if goal not met
✓ should allow refund if goal not met after deadline
✓ should prevent refund if goal was met
✓ should prevent contributions after deadline
✓ should prevent double withdrawal
✓ should track multiple contributors

Run with:

npx hardhat test

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What I Learned

• Writing and deploying Solidity smart contracts with Hardhat v3
• Interacting with Ethereum using viem (TypeScript-first alternative to ethers.js)
• Building a REST API that reads/writes to a live blockchain
• Reentrancy attack patterns and how to prevent them
• Working with BigInt for on-chain numeric values
• Sepolia testnet deployment and Etherscan verification

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Author

Parth Gohil
PGD in Backend & Blockchain Development — York University
GitHub

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Built on Ethereum Sepolia · Not for production use