Crowdfunding DApp (Web3)

A decentralized crowdfunding platform built with Solidity, Hardhat, Next.js, and ethers.js.

Features

• Create fundraising campaigns
• Donate ETH to campaigns
• Deadline-based fund locking
• Creator-only withdrawal if target is reached
• Refunds if target is not met
• Fully decentralized & trustless

Tech Stack

• Solidity (^0.8.x)
• Hardhat - Development environment & testing
• ethers.js (v6) - Ethereum library
• Next.js (App Router) - Frontend framework
• MetaMask - Wallet integration
• TypeScript - Type safety
• Tailwind CSS - Styling

Project Architecture

High-level Flow

User (Browser)
   ↓
Next.js Frontend (ethers.js)
   ↓
MetaMask (Signer)
   ↓
CrowdFunding Smart Contract
   ↓
Ethereum (Hardhat / Testnet)

Responsibilities

• Frontend: UI, validation, wallet UX
• MetaMask: Signing + user consent
• Smart Contract: Funds, rules, trust
• Blockchain: Source of truth

This separation is clean and interview-grade.

Smart Contract Design

• Funds are locked until campaign deadline
• Withdrawal allowed only if target is reached
• Refunds enabled if target is not met
• Reentrancy-safe logic
• Events emitted for indexing

Key Functions

• createCampaign() - Create a new fundraising campaign
• donateToCampaign() - Donate ETH to a campaign
• withdrawFunds() - Creator withdraws funds if target reached
• refund() - Donors get refund if target not met
• getCampaign() - Get campaign details
• getAllCampaigns() - Get all campaigns

Security Considerations

• State updates before external calls (Checks-Effects-Interactions pattern)
• Access control on withdrawals (only creator can withdraw)
• Built-in overflow checks (Solidity 0.8.x)
• Pull-based refund pattern
• Campaign existence and active state modifiers
• Deadline validation

Running Locally

Prerequisites

• Node.js (v18+)
• npm or yarn
• MetaMask browser extension

1. Install Dependencies

npm install
cd frontend-app && npm install

2. Start Hardhat Node

npx hardhat node

This starts a local Ethereum node on http://localhost:8545 with 20 test accounts pre-funded with ETH.

3. Deploy Contract

In a new terminal:

npx hardhat run scripts/deploy.js --network localhost

Copy the deployed contract address and update it in frontend-app/config.js.

4. Configure MetaMask

• Network Name: Hardhat Local
• RPC URL: http://127.0.0.1:8545
• Chain ID: 31337
• Currency Symbol: ETH

5. Import Test Account

Import one of the Hardhat test accounts into MetaMask:

• Account #0: 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80
• Account #1: 0x59c6995e998f97a5a0044966f0945389dc9e86dae88c7a8412f4603b6b78690d

6. Start Frontend

cd frontend-app
npm run dev

Open http://localhost:3000 in your browser.

Sepolia Testnet Deployment

The contract is deployed on Sepolia testnet:

Contract Address: 0xAff0367646b6cCC707057e4e32d83daF8C0c0772

Deploying to Sepolia

1. Get Sepolia ETH from Sepolia Faucet

2. Create .env file in the root directory:

SEPOLIA_RPC_URL=https://sepolia.infura.io/v3/YOUR_KEY
PRIVATE_KEY=0xYOUR_PRIVATE_KEY

3. Deploy:

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

4. Update frontend .env.local:

NEXT_PUBLIC_CONTRACT_ADDRESS=0xAff0367646b6cCC707057e4e32d83daF8C0c0772

5. Switch MetaMask to Sepolia network and test!

Testing

Run the test suite:

npx hardhat test

Test coverage includes:

• Campaign creation
• Donations
• Withdrawals
• Refunds
• Edge cases and error handling

Project Structure

crowdfunding-dapp/
├── contracts/
│   └── CrowdFunding.sol      # Main smart contract
├── scripts/
│   └── deploy.js              # Deployment script
├── test/
│   ├── campaign-create-test.js
│   ├── campaign-donate-test.js
│   ├── campaign-withdraw-refund-test.js
│   ├── campaign-getters-test.js
│   └── campaign-edgecases-test.js
├── frontend-app/
│   ├── app/
│   │   ├── page.tsx          # Main UI component
│   │   └── layout.tsx        # App layout
│   ├── abi/
│   │   └── CrowdFunding.json # Contract ABI
│   └── config.js             # Contract address & config
├── hardhat.config.js          # Hardhat configuration
└── README.md                  # This file

Future Improvements

• Testnet deployment (Sepolia/Goerli)
• The Graph indexing for efficient campaign queries
• Better UI with enhanced Tailwind components
• Campaign images & categories (IPFS integration)
• DAO / multisig withdrawals for added security
• Campaign search and filtering
• Donor leaderboards
• Email notifications for campaign updates
• Gas optimization improvements

Interview Narrative

"Tell me about your project"

"I built a decentralized crowdfunding DApp where users can create campaigns, donate ETH, and withdraw funds only if the target is reached after a deadline.

The smart contract enforces trust: funds are locked, creators can't rug-pull, and donors can refund if goals aren't met.

I wrote comprehensive unit tests, handled MetaMask UX, and focused on security like reentrancy protection and access control."

Scaling Answers

"How would you scale this?"

• Use The Graph to index campaigns and events for efficient queries
• Cache reads with read-only provider to reduce RPC calls
• Add IPFS for campaign metadata (images, descriptions)
• Implement DAO / multisig for withdrawals on high-value campaigns
• Add rate limiting on frontend to prevent spam
• Use Layer 2 solutions (Polygon, Arbitrum) for lower gas costs
• Implement batching for multiple donations

Author

Built by Shubham

License

MIT