Making a full-stack DeFi app with Polygon

DeFi is now a serious matter of dialogue within the cryptocurrency area. DeFi stands for “Decentralized finance,” which implies that there’s no central authority keeping track of and controlling the switch of funds. This additionally implies that transactions in DeFi are P2P (peer to look), which implies that no central authority is liable for transferral, and funds are despatched straight from one entity to a different.

On this article we are going to discover ways to get began with DeFi by making a full-stack DeFi app on the Polygon chain utilizing Subsequent.js because the frontend. This app will promote and buy OKToken (a fictional token) from the consumer. Nonetheless, each buy transaction reduces one token from the quantity of tokens you may get per MATIC (promoting will increase this quantity by one). This isn’t a really perfect demonstration, however this fashion you possibly can perceive use your individual logic in Solidity good contracts and study to create your individual full-stack DeFi app utilizing Polygon.

Contents

Necessities

To get began with this tutorial, be sure you have the next:

Now that you’ve checked the necessities, let’s proceed with creating our Hardhat venture to work with our Solidity good contracts.

Making a Hardhat venture

Navigate to a secure listing and run the next command within the terminal to initialize your Hardhat venture:

npx hardhat

When you run the command, you need to see the next Hardhat initialization wizard in your terminal.

From the listing, select Create a complicated pattern venture. Then you can be requested the place you wish to initialize the Hardhat venture; don’t change the sphere, simply press Enter in order that the venture will get initialized within the present listing.

Then you can be requested whether or not or not you wish to set up dependencies required to your Hardhat venture to run. Press y as a result of we shall be needing these dependencies, and putting in them proper now’s the perfect thought.

Set up of dependencies will begin, and would possibly take just a few seconds or minutes relying upon the machine you’re operating. Now, run the next command within the terminal to put in one other dependency we might want to ease our Solidity contract growth:

npm set up @openzeppelin/contracts

OpenZeppelin gives good contract requirements that we will use in our personal good contracts to simply create an Ownable, ERC-20 and ERC-721 contracts, and extra.

As soon as the dependencies are efficiently put in, open the listing in a code editor. I’ll be utilizing VS Code for this tutorial.

We shall be creating two good contracts: the primary one shall be our ERC-20 token itself and the second shall be a vendor contract, which is able to facilitate shopping for and promoting of those tokens.

Creating our good contracts

Now, go to the contracts folder and create a brand new Solidity file named OKToken.sol, which is able to comprise our ERC-20 token contract.

Use the next code for this file:

// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.4;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract OKToken is ERC20 {
    constructor() ERC20("OKT", "OKToken"){
        _mint(msg.sender, 10000 * 10 ** 18);
    }
}

Within the above code, we’re importing the ERC20.sol file from @openzeppelin/contracts which is able to assist us get began with an ERC-20 token simply. Then, within the constructor, we’re offering the image "OKT" and title "OKToken" for our token.

That’s all for the token contract! Now, let’s work on the seller contract. Underneath the contracts folder, create a brand new file named OKVendor.sol with the next code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;
import "./OKToken.sol";
import "@openzeppelin/contracts/entry/Ownable.sol";

contract OKVendor is Ownable {
  OKToken yourToken;
  uint256 public tokensPerNativeCurrency = 100;
  occasion BuyTokens(tackle purchaser, uint256 amountOfNativeCurrency, uint256 amountOfTokens);
  constructor(tackle tokenAddress) {
    yourToken = OKToken(tokenAddress);
  }

  perform buyTokens() public payable returns (uint256 tokenAmount) {
    require(msg.worth > 0, "You have to ship some NativeCurrency to proceed");
    uint256 amountToBuy = msg.worth * tokensPerNativeCurrency;

    uint256 vendorBalance = yourToken.balanceOf(tackle(this));
    require(vendorBalance >= amountToBuy, "Vendor contract has not sufficient tokens to carry out transaction");

    (bool despatched) = yourToken.switch(msg.sender, amountToBuy);
    require(despatched, "Did not switch token to consumer");
    tokensPerNativeCurrency = tokensPerNativeCurrency - 1;

    emit BuyTokens(msg.sender, msg.worth, amountToBuy);
    return amountToBuy;
  }
  perform sellTokens(uint256 tokenAmountToSell) public {

    require(tokenAmountToSell > 0, "Specify an quantity of token higher than zero");

    uint256 userBalance = yourToken.balanceOf(msg.sender);
    require(userBalance >= tokenAmountToSell, "You've inadequate tokens");

    uint256 amountOfNativeCurrencyToTransfer = tokenAmountToSell / tokensPerNativeCurrency;
    uint256 ownerNativeCurrencyBalance = tackle(this).steadiness;
    require(ownerNativeCurrencyBalance >= amountOfNativeCurrencyToTransfer, "Vendor has inadequate funds");
    (bool despatched) = yourToken.transferFrom(msg.sender, tackle(this), tokenAmountToSell);
    require(despatched, "Did not switch tokens from consumer to vendor");

    (despatched,) = msg.sender.name{worth: amountOfNativeCurrencyToTransfer}("");
    tokensPerNativeCurrency = tokensPerNativeCurrency + 1;
    require(despatched, "Did not ship NativeCurrency to the consumer");
  }
  perform getNumberOfTokensInNativeCurrency() public view returns(uint256) {
    return tokensPerNativeCurrency;
  }

  perform withdraw() public onlyOwner {
    uint256 ownerBalance = tackle(this).steadiness;
    require(ownerBalance > 0, "No NativeCurrency current in Vendor");
    (bool despatched,) = msg.sender.name{worth: tackle(this).steadiness}("");
    require(despatched, "Did not withdraw");
  }
}

It will assist us facilitate the shopping for and promoting of tokens.

Within the above contract, first we’re importing our token contract, which we want in an effort to work together with our token contract utilizing the seller contract and name capabilities.

We’re additionally importing Ownable.sol from @openzeppelin/contracts. Which means that the proprietor of the good contract can switch its possession and have entry to owners-only capabilities.

After initializing the good contract, we outline the variable tokensPerNativeCurrency which states the variety of tokens which might be bought utilizing 1 MATIC. We shall be altering this quantity primarily based on the transactions made.

We then have a constructor which is able to take OKToken’s contract tackle in order that we will talk with the deployed contract and carry out capabilities on them.

Within the buyTokens() perform, we’re performing checks to make sure the right quantity of MATIC is shipped to the good contract, and that the seller contract has the required quantity of tokens. Then we name the perform switch() from the OKToken occasion we beforehand created to switch the tokens to the request sender.

Within the sellTokens() perform, we’re performing checks to make sure that the request sender has sufficient tokens and if the seller contract has sufficient MATIC to ship again to the request sender. Then, we use the transferFrom() perform from the OKToken occasion we beforehand created to switch the tokens from the request sender’s pockets to the good contract. Nonetheless, the sender must approve this transaction; we carry out this approval on the shopper facet earlier than making the request. We’ll cowl this half after we make the entrance finish of this software.

Lastly, we now have the withdraw() perform, which is simply accessible by the proprietor of the contracts. It permits them to withdraw all of the MATIC current on the contract.

Now that we now have the good contracts prepared, let’s deploy them to Polygon Mumbai testnet!

Deploying our good contracts

We shall be making a script to deploy our contract to Polygon Mumbai. As soon as the contracts are deployed, we are going to programmatically ship all of the tokens saved on the deployer’s pockets to the seller contract.

First go to hardhat.config.js and underneath module.exports, add the next object in order that Hardhat is aware of which community to connect with:

networks: {
  mumbai: {
    url: "https://matic-mumbai.chainstacklabs.com",
    accounts: ["PRIVATE KEY HERE"],
  }
}

We’re offering the community a reputation (mumbai on this case) and offering an RPC URL. The talked about RPC URL is for Polygon Mumbai. If you wish to use Polygon Mainnet you possibly can select your RPC URL. Keep in mind to enter your individual pockets non-public key with some check MATIC to pay for fuel charges concerned within the good contract deployment course of.

Now, underneath the scripts folder, create a brand new file known as deploy.js. Paste within the following:

const { BigNumber, utils } = require("ethers");
const hardhat = require("hardhat");
async perform important() {
  const OKToken = await hardhat.ethers.getContractFactory("OKToken");
  const oktoken = await OKToken.deploy();
  await oktoken.deployed();
  console.log("[📥] OKToken deployed to handle: " + oktoken.tackle);
  const OKVendor = await hardhat.ethers.getContractFactory("OKVendor");
  const okvendor = await OKVendor.deploy(oktoken.tackle);
  console.log("[📥] OKVendor deployed to handle: " + okvendor.tackle);
  await oktoken.deployed();
  // Switch oktokens to vendor
  await oktoken.capabilities.switch(okvendor.tackle, utils.parseEther("10000"));
  console.log("[🚀] Tokens transferred to OKVendor");
}
important()
  .then(() => course of.exit(0))
  .catch((error) => {
    console.error(error);
    course of.exit(1);
});

Within the above file, we’re instructing Hardhat deploy our contract. The important() perform is the entry level right here. First, we get the OKToken contract and deploy it. Then, we get the OKVendor contract, present OKToken contract tackle within the constructor, and deploy the contract. Then, we switch all of the funds from OKToken contract to OKVendor contract.

Run the next command within the terminal to run the script and deploy our contracts to the Polygon Mumbai community:

npx hardhat run --network mumbai scripts/deploy.js --show-stack-traces

Notice that the community title should match the one talked about in hardhat.config.js. After operating the script, the contracts must be deployed and you need to see the next in your terminal:

In case you see an output much like this, your good contracts have been deployed and configured efficiently. Now, let’s proceed with creating our Subsequent.js software.

Making a Subsequent.js DeFi app

Underneath the identical listing, run the next command within the terminal to create your Subsequent.js app:

npx create-next-app frontend

The above command will create a brand new app and mechanically set up obligatory dependencies.

Navigate to the frontend folder and use the next command within the terminal to put in extra dependencies, which is able to assist us work together with our good contracts:

yarn add @thirdweb-dev/react @thirdweb-dev/sdk ethers web3

We’re putting in @thirdweb-dev/react and @thirdweb-dev/sdk in order that we will simply authenticate the consumer and join their wallets to our app utilizing MetaMask. ethers is a required dependency for thirdweb so we have to set up that as properly. Lastly, we’re putting in web3 in order that we will work together with our good contract.

Including the thirdweb supplier

To get began, we have to wrap our app inside a thirdwebProvider in order that thirdweb can perform correctly.

Go to your _app.js file underneath pages folder and add within the following:

import { thirdwebProvider, ChainId } from "@thirdweb-dev/react";
import "../types/globals.css";
perform MyApp({ Part, pageProps }) {
  return (
    <thirdwebProvider desiredChainId={ChainId.Mumbai}>
      <Part {...pageProps} />
    </thirdwebProvider>
  );
}
export default MyApp;

Within the above code, we’re importing thirdwebProvider and enclosing our app inside it. We’re additionally offering a desiredChainId of the chain ID of Polygon Mumbai. You can even use the chain ID for Polygon Mainnet if you want to take action.

Create a brand new file in your Subsequent.js app root known as contracts.js and add the next content material:

export const oktoken = {
  contractAddress: "0xE83DD81890C76BB8c4b8Bc6365Ad95E5e71495E5",
  abi: [
    {
      inputs: [],
      stateMutability: "nonpayable",
      sort: "constructor",
    },
    {
      nameless: false,
      inputs: [
        {
          indexed: true,
          internalType: "address",
          name: "owner",
          type: "address",
        },
        {
          indexed: true,
          internalType: "address",
          name: "spender",
          type: "address",
        },
        {
          indexed: false,
          internalType: "uint256",
          name: "value",
          type: "uint256",
        },
      ],
      title: "Approval",
      sort: "occasion",
    },
    {
      nameless: false,
      inputs: [
        {
          indexed: true,
          internalType: "address",
          name: "from",
          type: "address",
        },
        {
          indexed: true,
          internalType: "address",
          name: "to",
          type: "address",
        },
        {
          indexed: false,
          internalType: "uint256",
          name: "value",
          type: "uint256",
        },
      ],
      title: "Switch",
      sort: "occasion",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "owner",
          type: "address",
        },
        {
          internalType: "address",
          name: "spender",
          type: "address",
        },
      ],
      title: "allowance",
      outputs: [
        {
          internalType: "uint256",
          name: "",
          type: "uint256",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "spender",
          type: "address",
        },
        {
          internalType: "uint256",
          name: "amount",
          type: "uint256",
        },
      ],
      title: "approve",
      outputs: [
        {
          internalType: "bool",
          name: "",
          type: "bool",
        },
      ],
      stateMutability: "nonpayable",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "account",
          type: "address",
        },
      ],
      title: "balanceOf",
      outputs: [
        {
          internalType: "uint256",
          name: "",
          type: "uint256",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [],
      title: "decimals",
      outputs: [
        {
          internalType: "uint8",
          name: "",
          type: "uint8",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "spender",
          type: "address",
        },
        {
          internalType: "uint256",
          name: "subtractedValue",
          type: "uint256",
        },
      ],
      title: "decreaseAllowance",
      outputs: [
        {
          internalType: "bool",
          name: "",
          type: "bool",
        },
      ],
      stateMutability: "nonpayable",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "spender",
          type: "address",
        },
        {
          internalType: "uint256",
          name: "addedValue",
          type: "uint256",
        },
      ],
      title: "increaseAllowance",
      outputs: [
        {
          internalType: "bool",
          name: "",
          type: "bool",
        },
      ],
      stateMutability: "nonpayable",
      sort: "perform",
    },
    {
      inputs: [],
      title: "title",
      outputs: [
        {
          internalType: "string",
          name: "",
          type: "string",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [],
      title: "image",
      outputs: [
        {
          internalType: "string",
          name: "",
          type: "string",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [],
      title: "totalSupply",
      outputs: [
        {
          internalType: "uint256",
          name: "",
          type: "uint256",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "to",
          type: "address",
        },
        {
          internalType: "uint256",
          name: "amount",
          type: "uint256",
        },
      ],
      title: "switch",
      outputs: [
        {
          internalType: "bool",
          name: "",
          type: "bool",
        },
      ],
      stateMutability: "nonpayable",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "from",
          type: "address",
        },
        {
          internalType: "address",
          name: "to",
          type: "address",
        },
        {
          internalType: "uint256",
          name: "amount",
          type: "uint256",
        },
      ],
      title: "transferFrom",
      outputs: [
        {
          internalType: "bool",
          name: "",
          type: "bool",
        },
      ],
      stateMutability: "nonpayable",
      sort: "perform",
    },
  ],
};
export const okvendor = {
  contractAddress: "0xAa3b8cbB24aF3EF68a0B1760704C969E57c53D7A",
  abi: [
    {
      inputs: [
        {
          internalType: "address",
          name: "tokenAddress",
          type: "address",
        },
      ],
      stateMutability: "nonpayable",
      sort: "constructor",
    },
    {
      nameless: false,
      inputs: [
        {
          indexed: false,
          internalType: "address",
          name: "buyer",
          type: "address",
        },
        {
          indexed: false,
          internalType: "uint256",
          name: "amountOfNativeCurrency",
          type: "uint256",
        },
        {
          indexed: false,
          internalType: "uint256",
          name: "amountOfTokens",
          type: "uint256",
        },
      ],
      title: "BuyTokens",
      sort: "occasion",
    },
    {
      nameless: false,
      inputs: [
        {
          indexed: true,
          internalType: "address",
          name: "previousOwner",
          type: "address",
        },
        {
          indexed: true,
          internalType: "address",
          name: "newOwner",
          type: "address",
        },
      ],
      title: "OwnershipTransferred",
      sort: "occasion",
    },
    {
      inputs: [],
      title: "buyTokens",
      outputs: [
        {
          internalType: "uint256",
          name: "tokenAmount",
          type: "uint256",
        },
      ],
      stateMutability: "payable",
      sort: "perform",
    },
    {
      inputs: [],
      title: "getNumberOfTokensInNativeCurrency",
      outputs: [
        {
          internalType: "uint256",
          name: "",
          type: "uint256",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [],
      title: "proprietor",
      outputs: [
        {
          internalType: "address",
          name: "",
          type: "address",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [],
      title: "renounceOwnership",
      outputs: [],
      stateMutability: "nonpayable",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "uint256",
          name: "tokenAmountToSell",
          type: "uint256",
        },
      ],
      title: "sellTokens",
      outputs: [],
      stateMutability: "nonpayable",
      sort: "perform",
    },
    {
      inputs: [],
      title: "tokensPerNativeCurrency",
      outputs: [
        {
          internalType: "uint256",
          name: "",
          type: "uint256",
        },
      ],
      stateMutability: "view",
      sort: "perform",
    },
    {
      inputs: [
        {
          internalType: "address",
          name: "newOwner",
          type: "address",
        },
      ],
      title: "transferOwnership",
      outputs: [],
      stateMutability: "nonpayable",
      sort: "perform",
    },
    {
      inputs: [],
      title: "withdraw",
      outputs: [],
      stateMutability: "nonpayable",
      sort: "perform",
    },
  ],
};

Keep in mind to exchange the contract addresses with your individual in order that the Subsequent.js app tries to connect with the right good contract.

Now let’s begin coding up our app. Open index.js file underneath pages folder and add the next:

import { useAddress, useContract, useMetamask } from "@thirdweb-dev/react";
import Head from "subsequent/head";
import Picture from "subsequent/picture";
import { oktoken, okvendor } from "../contracts";
import types from "../types/Residence.module.css";
import { useEffect, useState } from "react";
import Web3 from "web3";
const web3 = new Web3(Web3.givenProvider);
export default perform Residence() {
  const [tokensPerCurrency, setTokensPerCurrency] = useState(0);
  const [tokens, setTokens] = useState(0);
  const tackle = useAddress();
  const connectUsingMetamask = useMetamask();
  const account = web3.defaultAccount;
  const buy = async () => {
    const contract = new web3.eth.Contract(
      okvendor.abi,
      okvendor.contractAddress
    );
    const ethToSend = tokens / tokensPerCurrency;
    const buy = await contract.strategies.buyTokens().ship({
      from: tackle,
      worth: web3.utils.toWei(ethToSend.toString(), "ether"),
    });
    console.log(buy);
    await fetchPrice();
  };
  const promote = async () => {
    const vendorContract = new web3.eth.Contract(
      okvendor.abi,
      okvendor.contractAddress
    );
    const tokenContract = new web3.eth.Contract(
      oktoken.abi,
      oktoken.contractAddress
    );
    const approve = await tokenContract.strategies
      .approve(
        okvendor.contractAddress,
        web3.utils.toWei(tokens.toString(), "ether")
      )
      .ship({
        from: tackle,
      });
    const sellTokens = await vendorContract.strategies.sellTokens(tokens).ship({
      from: tackle,
    });
    await fetchPrice();
  };
  const fetchPrice = async () => {
    const contract = new web3.eth.Contract(
      okvendor.abi,
      okvendor.contractAddress
    );
    const priceFromContract = await contract.strategies
      .getNumberOfTokensInNativeCurrency()
      .name();
    setTokensPerCurrency(priceFromContract);
  };
  useEffect(() => {
    fetchPrice();
  }, []);
  return (
    <div>
      <Head>
        <title>Change OKTokens</title>
      </Head>
      {tackle ? (
        <div>
          <p>Tokens per forex: {tokensPerCurrency}</p>
          <div>
            <enter
              sort="quantity"
              worth={tokens}
              onChange={(e) => setTokens(e.goal.worth)}
            />
          </div>
          <button onClick={buy}>Buy</button>
          <button onClick={promote}>Promote</button>
        </div>
      ) : (
        <div>
          <button onClick={connectUsingMetamask}>Join utilizing MetaMask</button>
        </div>
      )}
    </div>
  );
}

It is a lengthy code block, so let’s see what the code is doing step-by-step:

• Initializing the web3 package deal utilizing a supplier arrange by thirdweb
• Utilizing thirdweb hooks useMetamask() to authenticate and useAddress() to verify authentication state, then rendering the login button if the consumer doesn’t have pockets linked utilizing MetaMask
• Setting varied states to map textual content bins in our app
• Making a fetchPrice() perform to work together with our good contract and verify what number of tokens one MATIC can get, whereas additionally creating an useEffect to verify this worth at any time when the web page masses
• Making a buy() perform, which initializes our vendor contract and calls the buyTokens() perform from the contract, then sending some MATIC together with this transaction. Then, we name fetchPrice() in order that the most recent worth is proven

Lastly, we’re making a promote() perform, which initializes each token and vendor contract. First we work together with token contract’s approve() perform and permit the seller contract to switch funds on our behalf. We then are calling sellTokens() perform from the seller contract to lastly promote the tokens and obtain MATIC. We’re additionally calling fetchPrice() to get the most recent worth after transaction.

Our easy DeFi app is full! You possibly can view this app in your browser by operating the next command:

yarn dev

Now when you go to http://localhost:3000, you need to see the next display screen, and you need to be capable to make transactions.

Conclusion

This was a easy tutorial on create your individual full-stack DeFi app primarily based on Polygon. You possibly can implement your individual logic on the good contracts to make it even higher relying in your group. I counsel tinkering round with the code to be able to study in one of the simplest ways attainable.