# Token Contract 教學
>Ray Huang | Blockchain Developer
>Contact: [e-mail]

### ERC20
#### Token Standard
[EIP-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20)
[Openzeppelin docs](https://docs.openzeppelin.com/contracts/2.x/api/token/erc20)
[Openzeppelin implementation](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol)

// function
function name() public view returns (string)

function symbol() public view returns (string)

function decimals() public view returns (uint8)

function totalSupply() public view returns (uint256)

function balanceOf(address _owner) public view returns (uint256 balance)

function transfer(address _to, uint256 _value) public returns (bool success)

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)

function approve(address _spender, uint256 _value) public returns (bool success)

function allowance(address _owner, address _spender) public view returns (uint256 remaining)

// event
event Transfer(address indexed _from, address indexed _to, uint256 _value)

event Approval(address indexed _owner, address indexed _spender, uint256 _value)

#### Approve
 

#### Supplement
[SafeERC20](https://docs.openzeppelin.com/contracts/2.x/api/token/erc20#SafeERC20)
[ERC20 missing return value bug](https://twitter.com/Uniswap/status/1072286773554876416)

### ERC721
#### Token Standard
[EIP-721: Non-Fungible Token Standard](https://eips.ethereum.org/EIPS/eip-721)
[Openzeppelin docs](https://docs.openzeppelin.com/contracts/2.x/api/token/erc721)
[Openzeppelin implementation](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC721/ERC721.sol)
[ERC721Enumerable](https://docs.openzeppelin.com/contracts/2.x/api/token/erc721#ERC721Enumerable)
[ERC721Metadata](https://docs.openzeppelin.com/contracts/2.x/api/token/erc721#ERC721Metadata)

// function
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);

function supportsInterface(bytes4 interfaceID) external view returns (bool);

// event
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);

#### Supplement
[OpenSea Metadata Standards](https://docs.opensea.io/docs/metadata-standards)

{
  "description": "Friendly OpenSea Creature that enjoys long swims in the ocean.", 
  "external_url": "https://openseacreatures.io/3", 
  "image": "https://storage.googleapis.com/opensea-prod.appspot.com/puffs/3.png", 
  "name": "Dave Starbelly",
  "attributes": [ ... ]
}

[ERC721 explanation](https://anallergytoanalogy.medium.com/jumping-into-solidity-the-erc721-standard-part-4-ad21e3a5d9c)
[ERC721A](https://www.erc721a.org/)
[PlutoLab Interactive music NFT](https://opensea.io/assets/ethereum/0x63a2502977a7ee8b4345a9d8b8e10ad278c63d46/3272)

###### tags: `TEM 2022/11/17`