Building a Full-Stack DeFi App on Polygon

Decentralized finance (DeFi) has become a significant topic in the cryptocurrency space. DeFi applications aim to disrupt traditional financial systems by providing decentralized, secure, and transparent financial services. In this article, we will explore how to build a full-stack DeFi app on Polygon using Next.js as the frontend framework.

Prerequisites

Before we begin, make sure you have the following:

• Node.js installed
• VS Code installed
• Working knowledge of React and Next.js
• Working knowledge of Solidity and tools like Hardhat

Creating a Hardhat Project

To start building our DeFi app, we need to create a Hardhat project. Hardhat is a development environment for Ethereum smart contracts. Run the following command in your terminal to initialize a new Hardhat project:

npx hardhat init

Follow the prompts to set up your project. Once you’ve completed the setup, install the required dependencies:

npm install --save-dev @openzeppelin/contracts

Creating Smart Contracts

Create a new Solidity file called OKToken.sol in the contracts folder. This contract will represent our ERC-20 token:
“`solidity
pragma solidity ^0.8.0;

import “@openzeppelin/contracts/token/ERC20/ERC20.sol”;

contract OKToken is ERC20 {
constructor() public ERC20(“OKToken”, “OKT”) {}
}

Next, create a new Solidity file called `OKVendor.sol` in the `contracts` folder. This contract will facilitate buying and selling of our token:
solidity
pragma solidity ^0.8.0;

import “./OKToken.sol”;
import “@openzeppelin/contracts/access/Ownable.sol”;

contract OKVendor is Ownable {
// …
}
“`
Deploying Smart Contracts

Create a new file called deploy.js in the scripts folder. This script will deploy our smart contracts to the Polygon Mumbai testnet:
“`javascript
const { ethers } = require(“hardhat”);

async function main() {
const okTokenFactory = await ethers.getContractFactory(“OKToken”);
const okToken = await okTokenFactory.deploy();

const okVendorFactory = await ethers.getContractFactory(“OKVendor”);
const okVendor = await okVendorFactory.deploy(okToken.address);

// …
}

main();

Run the deployment script:

npx hardhat run scripts/deploy.js –network mumbai
“`
Creating a Next.js App

Create a new Next.js app in the same directory:

npx create-next-app frontend

Install the required dependencies:

npm install @thirdweb-dev/react @thirdweb-dev/sdk ethers web3

Adding Thirdweb Provider

Wrap your app with the Thirdweb provider in pages/_app.js:
“`javascript
import { ThirdwebProvider } from “@thirdweb-dev/react”;

function MyApp({ Component, pageProps }) {
return (


);
}

export default MyApp;

Create a new file called `contracts.js` in the root of your Next.js app:
javascript
export const okTokenAddress = “0x…”; // Replace with your OKToken contract address
export const okVendorAddress = “0x…”; // Replace with your OKVendor contract address
“`
Building the DeFi App

Create a new file called index.js in the pages folder:
“`javascript
import { useMetamask } from “@thirdweb-dev/react”;
import { useState, useEffect } from “react”;
import Web3 from “web3”;

const Home = () => {
const [userAddress, setUserAddress] = useState(“”);
const [tokenBalance, setTokenBalance] = useState(0);

const fetchPrice = async () => {
// …
};

const purchase = async () => {
// …
};

const sell = async () => {
// …
};

return (

);
};

export default Home;

Start the Next.js app:

npm run dev
“
Open your browser and navigate tohttp://localhost:3000`. You should see the DeFi app interface. Congratulations! You have successfully built a full-stack DeFi app on Polygon using Next.js.