How to Build a Full Stack NFT Marketplace - V2 (2022)
Tags: webdev, react, blockchain, web3
Published: 2021-07-06 15:14:09

---
title: How to Build a Full Stack NFT Marketplace - V2 (2022)
published: true
description: Building an NFT marketplace with Next.js, Tailwind, Solidity, and Polygon
tags: webdev, react, blockchain, web3
cover_image: https://dev-to-uploads.s3.amazonaws.com/uploads/articles/shlpjczbt9jrcbjwybzk.jpg
---

### Building an NFT marketplace with Polygon, Next.js, Tailwind, Solidity, Hardhat, Ethers.js, and IPFS

> To view the video course for this tutorial, click [here](https://www.youtube.com/watch?v=GKJBEEXUha0). To view Version 1 of this tutorial, click [here](https://gist.github.com/dabit3/ce61bb1593c9aeae31f2a31bcad7f5da)

In my last end to end Ethereum tutorial, [The Complete Guide to Full Stack Ethereum Development](https://dev.to/dabit3/the-complete-guide-to-full-stack-ethereum-development-3j13) I introduced how to build a basic app on Ethereum using modern tooling like [Hardhat](https://hardhat.org/) and [Ethers.js](https://docs.ethers.io/v5/).

In this guide you'll learn how to build, deploy, and test out a full stack NFT marketplace on Ethereum. We'll also look at how to deploy to Polygon.

One thing that has become apparent is how quickly Ethereum scaling solutions like [Polygon](https://polygon.technology/), [Arbitrum](https://developer.offchainlabs.com/docs/developer_quickstart), and [Optimism](https://optimism.io/) are gaining momentum and adoption. These technologies enable developers to build the same applications they would directly on Ethereum with the added benefits of lower gas costs and faster transaction speeds among other things.

Because of the value proposition that these solutions offer combined with the general lack of existing content, I will be building out various example projects and tutorials for full stack applications using these various Ethereum scaling solutions, starting with this one on Polygon.

> To view the final source code for this project, visit [this repo](https://github.com/dabit3/polygon-ethereum-nextjs-marketplace/)

### Prerequisites

To be successful in this guide, you must have the following:

1. Node.js version `16.14.0` or greater installed on your machine. I recommend installing Node using either [nvm](https://github.com/nvm-sh/nvm) or [fnm](https://github.com/Schniz/fnm).
2. Metamask wallet extension installed as a browser extension

### The stack

In this guide, we will build out a full stack application using:

__Web application framework__ - [Next.js](https://nextjs.org/)
__Solidity development environment__ - [Hardhat](https://hardhat.org/)
__File Storage__ - [IPFS](https://ipfs.io/)
__Ethereum Web Client Library__ - [Ethers.js](https://docs.ethers.io/v5/)

Though it will not be part of this guide (coming in a separate post), we will look at how to build a more robust API layer using [The Graph Protocol](https://thegraph.com/) to get around limitations in the data access patterns provided by the native blockchain layer.

### About the project

The project that we will be building will be __Metaverse Marketplace__ - an NFT marketplace.

![Metaverse Marketplace](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/lx8avrmuwqswx9roub2g.png)

When a user puts an NFT for sale, the ownership of the item will be transferred from the creator to the marketplace contract.

When a user purchases an NFT, the purchase price will be transferred from the buyer to the seller and the item will be transferred from the marketplace to the buyer.

The marketplace owner will be able to set a listing fee. This fee will be taken from the seller and transferred to the contract owner upon completion of any sale, enabling the owner of the marketplace to earn recurring revenue from any sale transacted in the marketplace.

The marketplace logic will consist of just one smart contract:

__NFT Marketplace Contract__ - [this](https://gist.github.com/dabit3/eb8866adc22bd86cabf5e6604b408e4a) contract allows users to mint NFTs and list them in a marketplace.

I believe this is a good project because the tools, techniques, and ideas we will be working with lay the foundation for many other types of applications on this stack – dealing with things like payments, commissions, and transfers of ownership on the contract level as well as how a client-side application would use this smart contract to build a performant and nice-looking user interface.

In addition to the smart contract, I'll also show you how to build a subgraph to make the querying of data from the smart contract more flexible and efficient. As you will see, creating views on data sets and enabling various and performant data access patterns is hard to do directly from a smart contract. [The Graph](https://thegraph.com/) makes this much easier.

### About Polygon

From [the docs](https://polygon.technology/):

___"Polygon is a protocol and a framework for building and connecting Ethereum-compatible blockchain networks. Aggregating scalable solutions on Ethereum supporting a multi-chain Ethereum ecosystem."___

[Polygon is about 10x faster than Ethereum & yet transactions are more than 10x cheaper](https://twitter.com/ChainLinkGod/status/1405688790241316864). 

Ok cool, but what does all that mean?

To me it means that _I can use the same knowledge, tools, and technologies I have been using to build apps on Ethereum to build apps that are faster and cheaper for users_, providing not only a better user experience but also opening the door for many types of applications that just would not be feasible to be built directly on Ethereum.

As mentioned before, there are many other Ethereum scaling solutions such as [Arbitrum](https://developer.offchainlabs.com/docs/developer_quickstart)and [Optimism](https://optimism.io/) that are also in a similar space. Most of these [scaling solutions](https://ethereum.org/en/developers/docs/scaling/) have technical differences and fall into various categories like [sidechains](https://ethereum.org/en/developers/docs/scaling/sidechains/) , [layer 2s](https://ethereum.org/en/developers/docs/scaling/layer-2-rollups/), and [state channels](https://ethereum.org/en/developers/docs/scaling/state-channels/).

Polygon [recently rebranded from Matic](https://cointelegraph.com/news/matic-rebrands-to-polygon-in-pursuit-of-polkadot-on-ethereum-strategy) so you will also see the word __Matic__ used interchangeably when referring to various parts of their ecosystem because the name still is being used in various places, like their token and network names.

To learn more about Polygon, check out [this post](https://medium.com/coinmonks/polygon-matic-could-it-win-the-eth-scaling-race-2c8b4e9baf51) as well as their documentation [here](https://docs.matic.network/docs/develop/getting-started).

Now that we have an overview of the project and related technologies, let's start building!

## Project setup

To get started, we'll create a new Next.js app. To do so, open your terminal. Create or change into a new empty directory and run the following command:

```sh
npx create-next-app nft-marketplace
```

Next, change into the new directory and install the dependencies using a package manager like `npm`, `yarn`, or `pnpm`:

```sh
cd nft-marketplace

npm install ethers hardhat @nomiclabs/hardhat-waffle \
ethereum-waffle chai @nomiclabs/hardhat-ethers \
web3modal @openzeppelin/contracts ipfs-http-client \
axios
```

### Setting up Tailwind CSS

We'll be using [Tailwind CSS](https://tailwindcss.com/) for styling, we we will set that up in this step.

Tailwind is a utility-first CSS framework that makes it easy to add styling and create good looking websites without a lot of work.

Next, install the Tailwind dependencies:

```sh
npm install -D tailwindcss@latest postcss@latest autoprefixer@latest
```

Next, we will create the configuration files needed for Tailwind to work with Next.js (`tailwind.config.js` and `postcss.config.js`) by running the following command:

```sh
npx tailwindcss init -p
```

Next, configure your template `content` paths in __tailwind.config.js__:

```javascript
/* tailwind.config.js */
module.exports = {
  content: [
    "./pages/**/*.{js,ts,jsx,tsx}",
    "./components/**/*.{js,ts,jsx,tsx}",
  ],
  theme: {
    extend: {},
  },
  plugins: [],
}
```

Finally, delete the code in __styles/globals.css__ and update it with the following:

```css
@tailwind base;
@tailwind components;
@tailwind utilities;
```

### Configuring Hardhat

Next, initialize a new Hardhat development environment from the root of your project:

```sh
npx hardhat

? What do you want to do? Create a basic sample project
? Hardhat project root: <Choose default path>
```

> If you get an error referencing your __README.md__, delete __README.md__ and run `npx hardhat` again.

Now you should see the following files and folders created for you in your root directory:

__hardhat.config.js__ - The entirety of your Hardhat setup (i.e. your config, plugins, and custom tasks) is contained in this file.
__scripts__ - A folder containing a script named sample-script.js that will deploy your smart contract when executed
__test__ - A folder containing an example testing script
__contracts__ - A folder holding an example Solidity smart contract

Next, update the configuration at __hardhat.config.js__ with the following:

> View the gist [here](https://gist.github.com/dabit3/9c4af9adeb3384e9ae3271181bce0f96)

```javascript
/* hardhat.config.js */
require("@nomiclabs/hardhat-waffle")

module.exports = {
  defaultNetwork: "hardhat",
  networks: {
    hardhat: {
      chainId: 1337
    },
//  unused configuration commented out for now
//  mumbai: {
//    url: "https://rpc-mumbai.maticvigil.com",
//    accounts: [process.env.privateKey]
//  }
  },
  solidity: {
    version: "0.8.4",
    settings: {
      optimizer: {
        enabled: true,
        runs: 200
      }
    }
  }
}
```

In this configuration, we've configured the local Hardhat development environment as well as the [__Mumbai testnet__](https://docs.matic.network/docs/develop/network-details/network/#mumbai-testnet) (commented out for now). 

You can read more about both Matic networks [here](https://docs.matic.network/docs/develop/network-details/network/).

### Smart Contract

Next, we'll create our smart contract!

In this file I'll do my best to comment within the code everything that is going on.

Create a new file in the __contracts__ directory named __NFTMarketplace.sol__. Here, add the following code:

> View the gist [here](https://gist.github.com/dabit3/eb8866adc22bd86cabf5e6604b408e4a)

```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

import "hardhat/console.sol";

contract NFTMarketplace is ERC721URIStorage {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;
    Counters.Counter private _itemsSold;

    uint256 listingPrice = 0.025 ether;
    address payable owner;

    mapping(uint256 => MarketItem) private idToMarketItem;

    struct MarketItem {
      uint256 tokenId;
      address payable seller;
      address payable owner;
      uint256 price;
      bool sold;
    }

    event MarketItemCreated (
      uint256 indexed tokenId,
      address seller,
      address owner,
      uint256 price,
      bool sold
    );

    constructor() ERC721("Metaverse Tokens", "METT") {
      owner = payable(msg.sender);
    }

    /* Updates the listing price of the contract */
    function updateListingPrice(uint _listingPrice) public payable {
      require(owner == msg.sender, "Only marketplace owner can update listing price.");
      listingPrice = _listingPrice;
    }

    /* Returns the listing price of the contract */
    function getListingPrice() public view returns (uint256) {
      return listingPrice;
    }

    /* Mints a token and lists it in the marketplace */
    function createToken(string memory tokenURI, uint256 price) public payable returns (uint) {
      _tokenIds.increment();
      uint256 newTokenId = _tokenIds.current();

      _mint(msg.sender, newTokenId);
      _setTokenURI(newTokenId, tokenURI);
      createMarketItem(newTokenId, price);
      return newTokenId;
    }

    function createMarketItem(
      uint256 tokenId,
      uint256 price
    ) private {
      require(price > 0, "Price must be at least 1 wei");
      require(msg.value == listingPrice, "Price must be equal to listing price");

      idToMarketItem[tokenId] =  MarketItem(
        tokenId,
        payable(msg.sender),
        payable(address(this)),
        price,
        false
      );

      _transfer(msg.sender, address(this), tokenId);
      emit MarketItemCreated(
        tokenId,
        msg.sender,
        address(this),
        price,
        false
      );
    }

    /* allows someone to resell a token they have purchased */
    function resellToken(uint256 tokenId, uint256 price) public payable {
      require(idToMarketItem[tokenId].owner == msg.sender, "Only item owner can perform this operation");
      require(msg.value == listingPrice, "Price must be equal to listing price");
      idToMarketItem[tokenId].sold = false;
      idToMarketItem[tokenId].price = price;
      idToMarketItem[tokenId].seller = payable(msg.sender);
      idToMarketItem[tokenId].owner = payable(address(this));
      _itemsSold.decrement();

      _transfer(msg.sender, address(this), tokenId);
    }

    /* Creates the sale of a marketplace item */
    /* Transfers ownership of the item, as well as funds between parties */
    function createMarketSale(
      uint256 tokenId
      ) public payable {
      uint price = idToMarketItem[tokenId].price;
      address seller = idToMarketItem[tokenId].seller;
      require(msg.value == price, "Please submit the asking price in order to complete the purchase");
      idToMarketItem[tokenId].owner = payable(msg.sender);
      idToMarketItem[tokenId].sold = true;
      idToMarketItem[tokenId].seller = payable(address(0));
      _itemsSold.increment();
      _transfer(address(this), msg.sender, tokenId);
      payable(owner).transfer(listingPrice);
      payable(seller).transfer(msg.value);
    }

    /* Returns all unsold market items */
    function fetchMarketItems() public view returns (MarketItem[] memory) {
      uint itemCount = _tokenIds.current();
      uint unsoldItemCount = _tokenIds.current() - _itemsSold.current();
      uint currentIndex = 0;

      MarketItem[] memory items = new MarketItem[](unsoldItemCount);
      for (uint i = 0; i < itemCount; i++) {
        if (idToMarketItem[i + 1].owner == address(this)) {
          uint currentId = i + 1;
          MarketItem storage currentItem = idToMarketItem[currentId];
          items[currentIndex] = currentItem;
          currentIndex += 1;
        }
      }
      return items;
    }

    /* Returns only items that a user has purchased */
    function fetchMyNFTs() public view returns (MarketItem[] memory) {
      uint totalItemCount = _tokenIds.current();
      uint itemCount = 0;
      uint currentIndex = 0;

      for (uint i = 0; i < totalItemCount; i++) {
        if (idToMarketItem[i + 1].owner == msg.sender) {
          itemCount += 1;
        }
      }

      MarketItem[] memory items = new MarketItem[](itemCount);
      for (uint i = 0; i < totalItemCount; i++) {
        if (idToMarketItem[i + 1].owner == msg.sender) {
          uint currentId = i + 1;
          MarketItem storage currentItem = idToMarketItem[currentId];
          items[currentIndex] = currentItem;
          currentIndex += 1;
        }
      }
      return items;
    }

    /* Returns only items a user has listed */
    function fetchItemsListed() public view returns (MarketItem[] memory) {
      uint totalItemCount = _tokenIds.current();
      uint itemCount = 0;
      uint currentIndex = 0;

      for (uint i = 0; i < totalItemCount; i++) {
        if (idToMarketItem[i + 1].seller == msg.sender) {
          itemCount += 1;
        }
      }

      MarketItem[] memory items = new MarketItem[](itemCount);
      for (uint i = 0; i < totalItemCount; i++) {
        if (idToMarketItem[i + 1].seller == msg.sender) {
          uint currentId = i + 1;
          MarketItem storage currentItem = idToMarketItem[currentId];
          items[currentIndex] = currentItem;
          currentIndex += 1;
        }
      }
      return items;
    }
}
```

In this contract we are inheriting from the [ERC721 standard](https://eips.ethereum.org/EIPS/eip-721) implemented by [OpenZepplin](https://docs.openzeppelin.com/contracts/2.x/api/token/erc721)

Now the smart contract code and environment is complete and we can try testing it out.

To do so, we can create a local test to run through much of the functionality, like minting a token, putting it up for sale, selling it to a user, and querying for tokens.

To create the test, open __test/sample-test.js__ and update it with the following code:

> View the gist [here](https://gist.github.com/dabit3/8d41d27c60b4f16b105bd2479013c172)

```javascript
/* test/sample-test.js */
describe("NFTMarket", function() {
  it("Should create and execute market sales", async function() {
    /* deploy the marketplace */
    const NFTMarketplace = await ethers.getContractFactory("NFTMarketplace")
    const nftMarketplace = await NFTMarketplace.deploy()
    await nftMarketplace.deployed()

    let listingPrice = await nftMarketplace.getListingPrice()
    listingPrice = listingPrice.toString()

    const auctionPrice = ethers.utils.parseUnits('1', 'ether')

    /* create two tokens */
    await nftMarketplace.createToken("https://www.mytokenlocation.com", auctionPrice, { value: listingPrice })
    await nftMarketplace.createToken("https://www.mytokenlocation2.com", auctionPrice, { value: listingPrice })
      
    const [_, buyerAddress] = await ethers.getSigners()
  
    /* execute sale of token to another user */
    await nftMarketplace.connect(buyerAddress).createMarketSale(1, { value: auctionPrice })

    /* resell a token */
    await nftMarketplace.connect(buyerAddress).resellToken(1, auctionPrice, { value: listingPrice })

    /* query for and return the unsold items */
    items = await nftMarketplace.fetchMarketItems()
    items = await Promise.all(items.map(async i => {
      const tokenUri = await nftMarketplace.tokenURI(i.tokenId)
      let item = {
        price: i.price.toString(),
        tokenId: i.tokenId.toString(),
        seller: i.seller,
        owner: i.owner,
        tokenUri
      }
      return item
    }))
    console.log('items: ', items)
  })
})
```

Next, run the test from your command line:

```sh
npx hardhat test
```

If the test runs successfully, it should log out an array containing the two marketplace items.

![Running the test](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/cewr5c4nkwudh8xd5etd.png)

## Building the front end

Now that the smart contract is working and ready to go, we can start building out the UI.

The first thing we might think about is setting up a layout so that we can enable some navigation that will persist across all pages.

To set this up, open __pages/_app.js__ and update it with the following code:

> View the gist [here](https://gist.github.com/dabit3/1c747a13b4da549272ddcc113b1b9c96)

```javascript
/* pages/_app.js */
import '../styles/globals.css'
import Link from 'next/link'

function MyApp({ Component, pageProps }) {
  return (
    <div>
      <nav className="border-b p-6">
        <p className="text-4xl font-bold">Metaverse Marketplace</p>
        <div className="flex mt-4">
          <Link href="/">
            <a className="mr-4 text-pink-500">
              Home
            </a>
          </Link>
          <Link href="/create-nft">
            <a className="mr-6 text-pink-500">
              Sell NFT
            </a>
          </Link>
          <Link href="/my-nfts">
            <a className="mr-6 text-pink-500">
              My NFTs
            </a>
          </Link>
          <Link href="/dashboard">
            <a className="mr-6 text-pink-500">
              Dashboard
            </a>
          </Link>
        </div>
      </nav>
      <Component {...pageProps} />
    </div>
  )
}

export default MyApp
```

The navigation has links for the home route as well as a page to sell an NFT, view the NFTs you have purchased, and a dashboard to see the NFTs you've listed.

#### Querying the contract for marketplace items

The next page we'll update is __pages/index.js__. This is the main entry-point of the app, and will be the view where we query for the NFTs for sale and render them to the screen.

> View the gist [here](https://gist.github.com/dabit3/f24480130555e3d505156aea3e2024a4)

```javascript
/* pages/index.js */
import { ethers } from 'ethers'
import { useEffect, useState } from 'react'
import axios from 'axios'
import Web3Modal from 'web3modal'

import {
  marketplaceAddress
} from '../config'

import NFTMarketplace from '../artifacts/contracts/NFTMarketplace.sol/NFTMarketplace.json'

export default function Home() {
  const [nfts, setNfts] = useState([])
  const [loadingState, setLoadingState] = useState('not-loaded')
  useEffect(() => {
    loadNFTs()
  }, [])
  async function loadNFTs() {
    /* create a generic provider and query for unsold market items */
    const provider = new ethers.providers.JsonRpcProvider()
    const contract = new ethers.Contract(marketplaceAddress, NFTMarketplace.abi, provider)
    const data = await contract.fetchMarketItems()

    /*
    *  map over items returned from smart contract and format 
    *  them as well as fetch their token metadata
    */
    const items = await Promise.all(data.map(async i => {
      const tokenUri = await contract.tokenURI(i.tokenId)
      const meta = await axios.get(tokenUri)
      let price = ethers.utils.formatUnits(i.price.toString(), 'ether')
      let item = {
        price,
        tokenId: i.tokenId.toNumber(),
        seller: i.seller,
        owner: i.owner,
        image: meta.data.image,
        name: meta.data.name,
        description: meta.data.description,
      }
      return item
    }))
    setNfts(items)
    setLoadingState('loaded') 
  }
  async function buyNft(nft) {
    /* needs the user to sign the transaction, so will use Web3Provider and sign it */
    const web3Modal = new Web3Modal()
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()
    const contract = new ethers.Contract(marketplaceAddress, NFTMarketplace.abi, signer)

    /* user will be prompted to pay the asking proces to complete the transaction */
    const price = ethers.utils.parseUnits(nft.price.toString(), 'ether')   
    const transaction = await contract.createMarketSale(nft.tokenId, {
      value: price
    })
    await transaction.wait()
    loadNFTs()
  }
  if (loadingState === 'loaded' && !nfts.length) return (<h1 className="px-20 py-10 text-3xl">No items in marketplace</h1>)
  return (
    <div className="flex justify-center">
      <div className="px-4" style={{ maxWidth: '1600px' }}>
        <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 pt-4">
          {
            nfts.map((nft, i) => (
              <div key={i} className="border shadow rounded-xl overflow-hidden">
                <img src={nft.image} />
                <div className="p-4">
                  <p style={{ height: '64px' }} className="text-2xl font-semibold">{nft.name}</p>
                  <div style={{ height: '70px', overflow: 'hidden' }}>
                    <p className="text-gray-400">{nft.description}</p>
                  </div>
                </div>
                <div className="p-4 bg-black">
                  <p className="text-2xl font-bold text-white">{nft.price} ETH</p>
                  <button className="mt-4 w-full bg-pink-500 text-white font-bold py-2 px-12 rounded" onClick={() => buyNft(nft)}>Buy</button>
                </div>
              </div>
            ))
          }
        </div>
      </div>
    </div>
  )
}
```

When the page loads, we query the smart contract for any NFTs that are still for sale and render them to the screen along with metadata about the items and a button for purchasing them.

#### Creating and listing NFTs

Next, let's create the page that allows users to create and list NFTs.

There are a few things happening in this page:

1. The user is able to upload and save files to IPFS
2. The user is able to create a new NFT
3. The user is able to set metadata and price of item and list it for sale on the marketplace

After the user creates and lists an item, they are re-routed to the main page to view all of the items for sale.

> View the gist [here](https://gist.github.com/dabit3/20068fb7938f51e1411c8257bfe4fc9d)

```javascript
/* pages/create-nft.js */
import { useState } from 'react'
import { ethers } from 'ethers'
import { create as ipfsHttpClient } from 'ipfs-http-client'
import { useRouter } from 'next/router'
import Web3Modal from 'web3modal'

const client = ipfsHttpClient('https://ipfs.infura.io:5001/api/v0')

import {
  marketplaceAddress
} from '../config'

import NFTMarketplace from '../artifacts/contracts/NFTMarketplace.sol/NFTMarketplace.json'

export default function CreateItem() {
  const [fileUrl, setFileUrl] = useState(null)
  const [formInput, updateFormInput] = useState({ price: '', name: '', description: '' })
  const router = useRouter()

  async function onChange(e) {
    /* upload image to IPFS */
    const file = e.target.files[0]
    try {
      const added = await client.add(
        file,
        {
          progress: (prog) => console.log(`received: ${prog}`)
        }
      )
      const url = `https://ipfs.infura.io/ipfs/${added.path}`
      setFileUrl(url)
    } catch (error) {
      console.log('Error uploading file: ', error)
    }  
  }
  async function uploadToIPFS() {
    const { name, description, price } = formInput
    if (!name || !description || !price || !fileUrl) return
    /* first, upload metadata to IPFS */
    const data = JSON.stringify({
      name, description, image: fileUrl
    })
    try {
      const added = await client.add(data)
      const url = `https://ipfs.infura.io/ipfs/${added.path}`
      /* after metadata is uploaded to IPFS, return the URL to use it in the transaction */
      return url
    } catch (error) {
      console.log('Error uploading file: ', error)
    }  
  }

  async function listNFTForSale() {
    const url = await uploadToIPFS()
    const web3Modal = new Web3Modal()
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()

    /* create the NFT */
    const price = ethers.utils.parseUnits(formInput.price, 'ether')
    let contract = new ethers.Contract(marketplaceAddress, NFTMarketplace.abi, signer)
    let listingPrice = await contract.getListingPrice()
    listingPrice = listingPrice.toString()
    let transaction = await contract.createToken(url, price, { value: listingPrice })
    await transaction.wait()
   
    router.push('/')
  }

  return (
    <div className="flex justify-center">
      <div className="w-1/2 flex flex-col pb-12">
        <input 
          placeholder="Asset Name"
          className="mt-8 border rounded p-4"
          onChange={e => updateFormInput({ ...formInput, name: e.target.value })}
        />
        <textarea
          placeholder="Asset Description"
          className="mt-2 border rounded p-4"
          onChange={e => updateFormInput({ ...formInput, description: e.target.value })}
        />
        <input
          placeholder="Asset Price in Eth"
          className="mt-2 border rounded p-4"
          onChange={e => updateFormInput({ ...formInput, price: e.target.value })}
        />
        <input
          type="file"
          name="Asset"
          className="my-4"
          onChange={onChange}
        />
        {
          fileUrl && (
            <img className="rounded mt-4" width="350" src={fileUrl} />
          )
        }
        <button onClick={listNFTForSale} className="font-bold mt-4 bg-pink-500 text-white rounded p-4 shadow-lg">
          Create NFT
        </button>
      </div>
    </div>
  )
}
```

#### Viewing only the NFTs purchased by the user

In the __NFTMarketplace.sol__ smart contract, we created a function named `fetchMyNFTs` that only returns the NFTs owned by the user.

In __pages/my-nfts.js__, we will use that function to fetch and render them.

This functionality is different than the query main __pages/index.js__ page because we need to ask the user for their address and use it in the contract, so the user will have to sign the transaction for it to be able to fetch them properly.

> View the gist [here](https://gist.github.com/dabit3/bc8f091b2c200311439cbf6997320c2b)

```javascript
/* pages/my-nfts.js */
import { ethers } from 'ethers'
import { useEffect, useState } from 'react'
import axios from 'axios'
import Web3Modal from 'web3modal'
import { useRouter } from 'next/router'

import {
  marketplaceAddress
} from '../config'

import NFTMarketplace from '../artifacts/contracts/NFTMarketplace.sol/NFTMarketplace.json'

export default function MyAssets() {
  const [nfts, setNfts] = useState([])
  const [loadingState, setLoadingState] = useState('not-loaded')
  const router = useRouter()
  useEffect(() => {
    loadNFTs()
  }, [])
  async function loadNFTs() {
    const web3Modal = new Web3Modal({
      network: "mainnet",
      cacheProvider: true,
    })
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()

    const marketplaceContract = new ethers.Contract(marketplaceAddress, NFTMarketplace.abi, signer)
    const data = await marketplaceContract.fetchMyNFTs()

    const items = await Promise.all(data.map(async i => {
      const tokenURI = await marketplaceContract.tokenURI(i.tokenId)
      const meta = await axios.get(tokenURI)
      let price = ethers.utils.formatUnits(i.price.toString(), 'ether')
      let item = {
        price,
        tokenId: i.tokenId.toNumber(),
        seller: i.seller,
        owner: i.owner,
        image: meta.data.image,
        tokenURI
      }
      return item
    }))
    setNfts(items)
    setLoadingState('loaded') 
  }
  function listNFT(nft) {
    router.push(`/resell-nft?id=${nft.tokenId}&tokenURI=${nft.tokenURI}`)
  }
  if (loadingState === 'loaded' && !nfts.length) return (<h1 className="py-10 px-20 text-3xl">No NFTs owned</h1>)
  return (
    <div className="flex justify-center">
      <div className="p-4">
        <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 pt-4">
          {
            nfts.map((nft, i) => (
              <div key={i} className="border shadow rounded-xl overflow-hidden">
                <img src={nft.image} className="rounded" />
                <div className="p-4 bg-black">
                  <p className="text-2xl font-bold text-white">Price - {nft.price} Eth</p>
                  <button className="mt-4 w-full bg-pink-500 text-white font-bold py-2 px-12 rounded" onClick={() => listNFT(nft)}>List</button>
                </div>
              </div>
            ))
          }
        </div>
      </div>
    </div>
  )
}
```

#### Dashboard

The next page we will be creating is the dashboard that will allow users to view all of the items they have listed.

This page will be using the `fetchItemsListed` function from the __NFTMarketplace.sol__ smart contract which returns only the items that match the address of the user making the function call.

Create a new file called __dashboard.js__ in the __pages__ directory with the following code:

> View the gist [here](https://gist.github.com/dabit3/68993c17eb4cbb1c2b6c8e9ced176a01)

```javascript
/* pages/dashboard.js */
import { ethers } from 'ethers'
import { useEffect, useState } from 'react'
import axios from 'axios'
import Web3Modal from 'web3modal'

import {
  marketplaceAddress
} from '../config'

import NFTMarketplace from '../artifacts/contracts/NFTMarketplace.sol/NFTMarketplace.json'

export default function CreatorDashboard() {
  const [nfts, setNfts] = useState([])
  const [loadingState, setLoadingState] = useState('not-loaded')
  useEffect(() => {
    loadNFTs()
  }, [])
  async function loadNFTs() {
    const web3Modal = new Web3Modal({
      network: 'mainnet',
      cacheProvider: true,
    })
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()

    const contract = new ethers.Contract(marketplaceAddress, NFTMarketplace.abi, signer)
    const data = await contract.fetchItemsListed()

    const items = await Promise.all(data.map(async i => {
      const tokenUri = await contract.tokenURI(i.tokenId)
      const meta = await axios.get(tokenUri)
      let price = ethers.utils.formatUnits(i.price.toString(), 'ether')
      let item = {
        price,
        tokenId: i.tokenId.toNumber(),
        seller: i.seller,
        owner: i.owner,
        image: meta.data.image,
      }
      return item
    }))

    setNfts(items)
    setLoadingState('loaded') 
  }
  if (loadingState === 'loaded' && !nfts.length) return (<h1 className="py-10 px-20 text-3xl">No NFTs listed</h1>)
  return (
    <div>
      <div className="p-4">
        <h2 className="text-2xl py-2">Items Listed</h2>
          <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 pt-4">
          {
            nfts.map((nft, i) => (
              <div key={i} className="border shadow rounded-xl overflow-hidden">
                <img src={nft.image} className="rounded" />
                <div className="p-4 bg-black">
                  <p className="text-2xl font-bold text-white">Price - {nft.price} Eth</p>
                </div>
              </div>
            ))
          }
        </div>
      </div>
    </div>
  )
}
```

#### Reselling a token

The final page we will be creating will allow users to resell an NFT they've purchased from someone else.

This page will be using the `resellToken` function from the __NFTMarketplace.sol__ smart contract.

> View the gist [here](https://gist.github.com/dabit3/d73a69da9c05cc31ecabfcfe68effc2d)

```javascript
/* pages/resell-nft.js */
import { useEffect, useState } from 'react'
import { ethers } from 'ethers'
import { useRouter } from 'next/router'
import axios from 'axios'
import Web3Modal from 'web3modal'

import {
  marketplaceAddress
} from '../config'

import NFTMarketplace from '../artifacts/contracts/NFTMarketplace.sol/NFTMarketplace.json'

export default function ResellNFT() {
  const [formInput, updateFormInput] = useState({ price: '', image: '' })
  const router = useRouter()
  const { id, tokenURI } = router.query
  const { image, price } = formInput

  useEffect(() => {
    fetchNFT()
  }, [id])

  async function fetchNFT() {
    if (!tokenURI) return
    const meta = await axios.get(tokenURI)
    updateFormInput(state => ({ ...state, image: meta.data.image }))
  }

  async function listNFTForSale() {
    if (!price) return
    const web3Modal = new Web3Modal()
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()

    const priceFormatted = ethers.utils.parseUnits(formInput.price, 'ether')
    let contract = new ethers.Contract(marketplaceAddress, NFTMarketplace.abi, signer)
    let listingPrice = await contract.getListingPrice()

    listingPrice = listingPrice.toString()
    let transaction = await contract.resellToken(id, priceFormatted, { value: listingPrice })
    await transaction.wait()
   
    router.push('/')
  }

  return (
    <div className="flex justify-center">
      <div className="w-1/2 flex flex-col pb-12">
        <input
          placeholder="Asset Price in Eth"
          className="mt-2 border rounded p-4"
          onChange={e => updateFormInput({ ...formInput, price: e.target.value })}
        />
        {
          image && (
            <img className="rounded mt-4" width="350" src={image} />
          )
        }
        <button onClick={listNFTForSale} className="font-bold mt-4 bg-pink-500 text-white rounded p-4 shadow-lg">
          List NFT
        </button>
      </div>
    </div>
  )
}
```

### Running the project

To run the project, we will need to have a deploy script to deploy the smart contracts to the blockchain network.

#### Deploying the contracts to a local network

When we created the project, Hardhat created an example deployment script at __scripts/sample-script.js__.

To make the purpose of this script more clear, update the name of __scripts/sample-script.js__ to __scripts/deploy.js__.

Next, update __scripts/deploy.js__ with the following code:

```javascript
const hre = require("hardhat");
const fs = require('fs');

async function main() {
  const NFTMarketplace = await hre.ethers.getContractFactory("NFTMarketplace");
  const nftMarketplace = await NFTMarketplace.deploy();
  await nftMarketplace.deployed();
  console.log("nftMarketplace deployed to:", nftMarketplace.address);

  fs.writeFileSync('./config.js', `
  export const marketplaceAddress = "${nftMarketplace.address}"
  `)
}

main()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });
```

This script will deploy the contract to the blockchain network and create a file named __config.js__ that will hold the address of the smart contract after it's been deployed.

We will first test this on a local network, then deploy it to the [Mumbai testnet](https://docs.matic.network/docs/develop/network-details/network/).

To spin up a local network, open your terminal and run the following command:

```sh
npx hardhat node
```

This should create a local network with 20 accounts.

![Hardhat node](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/s1spai8459exh7looei7.png)


Next, keep the node running and open a separate terminal window to deploy the contract.

In a separate window, run the following command:

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

When the deployment is complete, the CLI should print out the address of the contract that was deployed:

![Contract address](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/6fk3mb7gz46b2rl4upte.png)

You should also see the __config.js__ file populated with this smart contract address.

#### Importing accounts into MetaMask

You can import the accounts created by the node into your Metamask wallet to try out in the app.

Each of these accounts is seeded with 10000 ETH.

To import one of these accounts, first switch your MetaMask wallet network to Localhost 8545.

![Localhost Network](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/cgcicglserwmyx6vrexy.jpeg)

Next, in MetaMask click on __Import Account__ from the accounts menu:

![MetaMask import account](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/04rv5hdn8s2f7tkslpru.jpeg)

Copy then paste one of the __Private Keys__ logged out by the CLI and click __Import__. Once the account is imported, you should see some the Eth in the account:

![MetaMask account](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/xc5y4xa9htjymncovo2o.jpeg)

I'd suggest doing this with 2 or 3 accounts so that you have the ability to test out the various functionality between users.

#### Running the app

Now we can test out the app!

To start the app, run the following command in your CLI:

```sh
npm run dev
```

To test everything out, try listing an item for sale, then switching to another account and purchasing it.

## Deploying to Polygon

Now that we have the project up and running and tested locally, let's deploy to Polygon. We'll start by deploying to [Mumbai](https://docs.polygon.technology/docs/develop/network-details/network/), the Polygon test network.

The first thing we will need to do is save one of our __private keys__ from our wallet as an environment variable.

To get the private key, you can use one of the private keys given to you by Hardhat or you can export them directly from MetaMask.

![Private keys](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/zyd4cs7f3czfwyeh5513.png)

If you are on a Mac, you can set an environment variable from the command line like so (be sure to run the deploy script from this same terminal and session):

```sh
export privateKey="your-private-key"
```

> Private keys are never meant to be shared publicly under any circumstance. It is advised never to hardcode a private key in a file. If you do choose to do so, be sure to use a testing wallet and to never under any circumstances push a file containing a private key to source control or expose it publicly.

### Configuring the network

Next, we need to switch from the local test network to the [Mumbai Testnet](https://docs.matic.network/docs/develop/network-details/network/#mumbai-testnet).

To do so, we need to create and set the network configuration.

First, open MetaMask and click on __Settings__.

![MetaMask settings](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/175kmqy9dp4uw94sk14l.png)

Next, click on __Networks__ and then __Add Network__:

![New Network](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/d762mh6l545ce9hexugf.png)

Here, we will add the following configurations for the Mumbai test network as listed [here](https://docs.polygon.technology/docs/develop/network-details/network/):

Network Name: __Mumbai TestNet__
New RPC URL: __https://rpc-mumbai.maticvigil.com__
Chain ID: __80001__
Currency Symbol: __Matic__

Save this, then you should be able to switch to and use the new network!

Finally, you will need some testnet Matic tokens in order to interact with the applications.

To get these, you can visit the [Matic Faucet](https://faucet.matic.network/), inputting the address of the wallets that you would like to request the tokens.

### Deploying to the Matic / Polygon network

Now that you have some Matic tokens, you can deploy to the Polygon network!

To do so, be sure that the address associated with the private key you are deploying your contract with has received some Matic tokens in order to pay the gas fees for the transaction.

Also, be sure to uncomment the `mumbai` configuration in __hardhat.config.js__:

```javascript
    mumbai: {
      url: "https://rpc-mumbai.maticvigil.com",
      accounts: [process.env.privateKey]
    }
```

To deploy to Matic, run the following command:

```sh
npx hardhat run scripts/deploy.js --network mumbai
```

> If you run a deployment error, the public RPC may be congested. In production, it's recommended to use an RPC provider like [Infura](https://infura.io/), [Alchemy](https://www.alchemy.com/), [Quicknode](https://www.quicknode.com/), or [Figment DataHub](https://datahub.figment.io/).

Once the contracts have been deployed, update the `loadNFTs` function call in __pages/index.js__ to include the new RPC endpoint:

```javascript
/* pages/index.js */

/* old provider */
const provider = new ethers.providers.JsonRpcProvider()

/* new provider */
const provider = new ethers.providers.JsonRpcProvider("https://rpc-mumbai.maticvigil.com")
```

You should now be able to update the contract addresses in your project and test on the new network 🎉!

```sh
npm run dev
```

> If you run into an error, the contract address printed out to the console by hardhat could be incorrect due to a bug I've run into recently. You can get the correct contract addresses by visiting [https://mumbai.polygonscan.com/](https://mumbai.polygonscan.com/) and pasting in the address from which the contracts were deployed to see the most recent transactions and getting the contract addresses from the transaction data.

#### Deploying to Mainnet

To deploy to the main Matic / Polygon network, you can use the same steps we set up for the Mumbai test network.

The main difference is that you'll need to use an endpoint for Matic as well as import the network into your MetaMask wallet as listed [here](https://docs.matic.network/docs/develop/network-details/network/).

An example update in your project to make this happen might look like this:

```javascript
/* hardhat.config.js */

/* adding Matic main network config to existing config */
...
matic: {
  url: "https://rpc-mainnet.maticvigil.com",
  accounts: [privateKey]
}
...
```

Public RPCs like the one listed above may have traffic or rate-limits depending on usage. You can sign up for a dedicated free RPC URL using services like Infura, MaticVigil, QuickNode, Alchemy, Chainstack, or Ankr.

For example, using something like Infura:

```javascript
url: `https://polygon-mainnet.infura.io/v3/${infuraId}`
```

> To view the final source code for this project, visit [this repo](https://github.com/dabit3/polygon-ethereum-nextjs-marketplace/)

### Next steps

Congratulations! You've deployed a non-trivial app to Polygon.

The coolest thing about working with solutions like Polygon is how little extra work or learning I had to do compared to building directly on Ethereum. Almost all of the APIs and tooling in these layer 2's and sidechains remain the same, making any skills transferable across various platforms like Polygon. 

For the next steps, I'd suggest porting over the queries implemented in this app using [The Graph](https://thegraph.com/). The Graph will open up many more data access patterns including things like pagination, filtering, and sorting which are necessary for any real-world application.

I will also be publishing a tutorial showing how to use Polygon with The Graph in the coming weeks.