🎨 ERC721 NFTs

ERC721 is the standard for non-fungible tokens (NFTs) on the EVM: each token has a unique ID and is not interchangeable. Defined by EIP-721 .

🎯 Why ERC721

Uniqueness — Each token ID maps to one owner; ideal for art, collectibles, in-game items
Ecosystem — OpenSea , Rarible , and wallets treat ERC721 as the default NFT standard
Extensions — ERC721Enumerable , metadata (name, symbol, tokenURI)

📚 Core Interface


// Minimal interface (EIP-721)
interface IERC721 {
    function balanceOf(address owner) external view returns (uint256);
    function ownerOf(uint256 tokenId) external view returns (address);
    function safeTransferFrom(address from, address to, uint256 tokenId) external;
    function transferFrom(address from, address to, uint256 tokenId) external;
    function approve(address to, uint256 tokenId) external;
    function getApproved(uint256 tokenId) external view returns (address);
    function setApprovalForAll(address operator, bool approved) external;
    function isApprovedForAll(address owner, address operator) external view returns (bool);
 
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
}

Metadata is usually provided via ERC721Metadata: name(), symbol(), tokenURI(tokenId) (returns a URL to JSON with name, description, image).

📝 Minimal ERC721 Example

Using OpenZeppelin :


// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
 
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
 
contract MyNFT is ERC721, Ownable {
    uint256 private _nextTokenId;
 
    constructor() ERC721("MyNFT", "MNFT") {}
 
    function mint(address to) public onlyOwner returns (uint256) {
        uint256 tokenId = _nextTokenId++;
        _safeMint(to, tokenId);
        return tokenId;
    }
}

🔧 Reading NFT Data (ethers.js v6)


import { ethers } from 'ethers';
 
const provider = new ethers.JsonRpcProvider(process.env.RPC_URL);
const nftAddress = '0x...';
const abi = [
  'function ownerOf(uint256 tokenId) view returns (address)',
  'function tokenURI(uint256 tokenId) view returns (string)',
  'function balanceOf(address owner) view returns (uint256)'
];
 
const nft = new ethers.Contract(nftAddress, abi, provider);
const tokenId = 1n;
 
const owner = await nft.ownerOf(tokenId);
const tokenURI = await nft.tokenURI(tokenId);
 
// tokenURI often points to IPFS or HTTP JSON (name, description, image)
const meta = await fetch(tokenURI).then(r => r.json());
console.log(meta.name, meta.image);

🎨 ERC721 NFTs

🎯 Why ERC721

📚 Core Interface

📝 Minimal ERC721 Example

🔧 Reading NFT Data (ethers.js v6)

🔗 Resources