How To Build “Buy Me a Coffee” DeFi dApp Using Solidity

Blockchain technology enables innovative applications like a decentralized “Buy Me a Coffee” service. This guide will walk you through developing and deploying a smart contract development service for this purpose using Alchemy, Hardhat, Ethers.js, and the Ethereum Sepolia testnet. At the conclusion, you will understand how to use Hardhat to create, test, and implement smart contracts. Link MetaMask and Sepolia together via an Alchemy RPC endpoint. Use a faucet to obtain Sepolia ETH. Construct the application’s front end and communicate with the contract using Ethers.js.

Detailed steps for building “Buy Me a Coffee” DeFi dApp Using Solidity

Prerequisites

Before starting, ensure you have:

npm version 8.5.5 or higher.
node version 16.13.1 or higher.
An Alchemy account.

Step 1: Project Setup 1- Create a new directory and then navigate into it:

mkdir BuyMeACoffee-contracts cd BuyMeACoffee-contracts

2- Initialize a new npm project:

npm init -y

3- Install Hardhat:

npm install --save-dev hardhat

4- Generate a Hardhat project:

npx hardhat

Select “Create a JavaScript project” and agree to the defaults.

5- Verify the setup by running tests:

npx hardhat test

Step 2: Writing the Smart Contract 1. Create the smart contract file: Copy BuyMeACoffee.sol and replace its content with:

// SPDX-License-Identifier: Unlicense pragma solidity ^0.8.0; contract BuyMeACoffee 
{ 
     event NewMemo(address indexed from, uint256 timestamp, string name, string message);
      struct Memos { address from; uint256 timestamp; string name; string message; } 
     address payable owner; Memos[] memos; 
    constructor() { owner = payable(msg.sender); } 
    function fetchMemosDetails() public view returns (Memos[] memory) { return memos; } 
    function buyCoffees(string memory _name, string memory _message) public payable { 
        require(msg.value > 0, "can't buy coffee for free!");
        memos.push(Memos(msg.sender, block.timestamp, _name, _message)); emit NewMemo(msg.sender, block.timestamp, _name, _message); 
    } 
    function withdrawTips() public { 
        require(owner.send(address(this).balance)); 
    } 
}

Step 3: Testing the Contract 1- Create a test script: Copy buy-coffee.js and use the following code:

const hre = require("hardhat"); 
async function getBalance(address) { 
    const balanceBigInt = await hre.ethers.provider.getBalance(address); 
    return hre.ethers.utils.formatEther(balanceBigInt); 
} 
async function printBalances(addresses) { 
     for (const [index, address] of addresses.entries()) {
       console.log(Address ${index} balance: , 
       await getBalance(address)); 
     } 
} 
async function printMemos(memos) { 
    for (const memo of memos) { 
        console.log(At ${memo.timestamp}, ${memo.name} (${memo.from}) said: "${memo.message}"); 
    } 
} 
async function main() { 
    const [owner, tipper3, tipper2, tipper] = await hre.ethers.getSigners(); 
    const BuyMeACoffee = await hre.ethers.getContractFactory("BuyMeACoffee"); 
    const buyMeACoffee = await BuyMeACoffee.deploy(); await buyMeACoffee.deployed(); 
    console.log("BuyMeACoffee deployed to:", buyMeACoffee.address); 
    const addresses = [owner.address, tipper.address, buyMeACoffee.address]; 
    console.log("== start =="); await printBalances(addresses); 
    const tip = { value: hre.ethers.utils.parseEther("1") }; 
    await buyMeACoffee.connect(tipper).buyCoffees("Carolina", "You're the best!", tip); 
    await buyMeACoffee.connect(tipper2).buyCoffees("Vitto", "Amazing teacher", tip);
    await buyMeACoffee.connect(tipper3).buyCoffees("Kay", "I love my Proof of Knowledge", tip);
    console.log("== bought coffee =="); 
    await printBalances(addresses); 
    await buyMeACoffee.connect(owner).withdrawTips(); 
    console.log("== withdrawTips =="); 
    await printBalances(addresses); 
    console.log("== memos =="); 
    const memos = await buyMeACoffee.fetchMemosDetails(); 
    printMemos(memos); 
} main() .then(() => process.exit(0)) .catch((error) => { 
    console.error(error); process.exit(1); 
});

2- Run the script:

npx hardhat run scripts/buy-coffee.js

Step 4: Deploying to Sepolia Testnet 1- Create a deployment script:

Create scripts/deploy.js with:

const hre = require("hardhat"); 
 async function main() { 
     const BuyMeACoffee = await hre.ethers.getContractFactory("BuyMeACoffee"); 
     const buyMeACoffee = await BuyMeACoffee.deploy(); 
     await buyMeACoffee.deployed(); 
     console.log("BuyMeACoffee deployed to:", buyMeACoffee.address); 
 } main() .then(() => process.exit(0)) .catch((error) => { 
     console.error(error); process.exit(1); 
 });

2- Configure Hardhat for Sepolia: Edit hardhat.config.js*:*

require("@nomiclabs/hardhat-ethers"); 
require("@nomiclabs/hardhat-waffle"); 
require("dotenv").config(); 
const SEPOLIA_URL = process.env.SEPOLIA_URL; 
const PRIVATE_KEY = process.env.PRIVATE_KEY;     
module.exports = { 
    solidity: "0.8.4", 
    networks: { 
        sepolia: { url: SEPOLIA_URL, accounts: [PRIVATE_KEY] } 
    } 
};

3- Install dotenv:

npm install dotenv

4- Create a .env file:

touch .env

5- Add your Alchemy and MetaMask details:

SEPOLIA_URL=https://eth-sepolia.alchemyapi.io/v2/ PRIVATE_KEY=

Conclusion

Developing a decentralized “Buy Me a Coffee” dApp using Solidity enables secure, transparent microtransactions. This blockchain-based strategy reduces costs and boosts efficiency by removing middlemen and guaranteeing immutable and verifiable transactions. It is an ideal solution that supports decentralized finance and is ideal for small enterprises and content providers. Are you a smart contract developer ready to transform microtransactions? Join us in creating secure, transparent dApps and shaping the future of decentralized payment solutions. Start building today!

*References

- Ethereum Stack Exchange : https://ethereum.stackexchange.com/

- GitHub : https://github.com/