ERC721 Tokens

Introduction to ERC721 Tokens

ERC721 is a standard for non-fungible tokens, meaning that each token is verifiably unique from all other tokens, and has become the dominant standard for on-chain NFTs. All ERC721s have a unique tokenId that differentiates them from every other token in the set.

An ERC721-compatible token must implement all the following functions and events:

    function balanceOf(address _owner) external view returns (uint256);
    function ownerOf(uint256 _tokenId) external view returns (address);
    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external payable;
    function safeTransferFrom(address _from, address _to, uint256 _tokenId) external payable;
    function transferFrom(address _from, address _to, uint256 _tokenId) external payable;
    function approve(address _approved, uint256 _tokenId) external payable;
    function setApprovalForAll(address _operator, bool _approved) external;
    function getApproved(uint256 _tokenId) external view returns (address);
    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);

Best Practices

We recommend using OpenZeppelin's popular and trusted ERC721 implementation in your project. The source code can be found at ERC721.sol. You can use OpenZeppelin's ERC721 implementation in your project through the following steps:

1. Install the OpenZeppelin library in your project by running the command:

npm install @openzeppelin/contracts

2. Once installed, you can use the ERC721 implementation in the library by importing it like this:

// contracts/GameItem.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

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

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

    constructor() ERC721("GameItem", "ITM") {}

    function awardItem(address player, string memory tokenURI)
        public
        returns (uint256)
    {
        uint256 newItemId = _tokenIds.current();
        _mint(player, newItemId);
        _setTokenURI(newItemId, tokenURI);

        _tokenIds.increment();
        return newItemId;
    }
}

For more information on OpenZeppelin ERC-20 implementation, please read ERC721.

References

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