1. ERC20代币标准实现

根据EIP-20标准文档：https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md

pragma solidity ^0.4.24;

contract ERC20Token {
    string public tokenName;
    string public tokenSymbol;
    uint8 public decimalUnits;
    uint256 public totalSupply;

    mapping(address => uint256) public balances;
    mapping(address => mapping(address => uint256)) public allowances;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    constructor() public {
        tokenName = "DigitalCoin";
        tokenSymbol = "DGC";
        decimalUnits = 0;
        totalSupply = 50000;
        balances[msg.sender] = totalSupply;
    }

    function transfer(address to, uint256 amount) public returns (bool) {
        require(to != address(0));
        require(balances[msg.sender] >= amount);
        require(balances[to] + amount > balances[to]);

        balances[msg.sender] -= amount;
        balances[to] += amount;
        emit Transfer(msg.sender, to, amount);
        return true;
    }

    function transferFrom(address from, address to, uint256 amount) public returns (bool) {
        require(from != address(0));
        require(to != address(0));
        require(balances[from] >= amount);
        require(allowances[from][msg.sender] >= amount);
        require(balances[to] + amount > balances[to]);

        balances[from] -= amount;
        balances[to] += amount;
        allowances[from][msg.sender] -= amount;
        emit Transfer(from, to, amount);
        return true;
    }

    function approve(address spender, uint256 amount) public returns (bool) {
        allowances[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function remainingAllowance(address owner, address spender) public view returns (uint256) {
        return allowances[owner][spender];
    }
}

2. DApp开发流程

核心技术栈：

• web3.js
• Solidity
• Truffle框架：安装指南
• Ganache测试网络

标准开发流程：

1. 项目初始化
2. 智能合约开发
3. 合约编译、部署与测试
4. 前端与合约交互

环境搭建：

npm install -g truffle
truffle version

项目初始化：

mkdir my-dapp
cd my-dapp
truffle init
truffle unbox pet-shop

示例合约：PetAdoption.sol

pragma solidity ^0.4.24;

contract PetAdoption {
    address[16] public adopters;

    function adoptPet(uint petId) public returns (uint) {
        require(petId >= 0 && petId <= 15);
        adopters[petId] = msg.sender;
        return petId;
    }

    function getAdoptersList() public view returns (address[16]) {
        return adopters;
    }
}

部署脚本：2_deploy_contracts.js

var Adoption = artifacts.require("./PetAdoption.sol");

module.exports = function(deployer) {
  deployer.deploy(Adoption);
};

网络配置：truffle-config.js

module.exports = {
  networks: {
    development: {
      host: "127.0.0.1",
      port: 7545,
      network_id: "*"
    }
  }
};

部署命令：

truffle migrate

3. Web3交互示例

let contractInstance;
PetAdoption.deployed().then(instance => contractInstance = instance);

// 查询余额
web3.eth.getBalance("0x627306090abab3a6e1400e9345bc60c78a8bef57").then(balance => {
    console.log(web3.utils.fromWei(balance, "ether"));
});

// 账户列表
web3.eth.getAccounts().then(accounts => console.log(accounts));

// 发起交易
web3.eth.sendTransaction({
    from: accounts[0],
    to: accounts[1],
    value: web3.utils.toWei("1", "ether")
});

4. 代币合约实现

pragma solidity ^0.4.24;

contract CryptoToken {
    uint256 public constant INITIAL_SUPPLY = 20000;
    mapping(address => uint256) public balances;

    constructor() public {
        balances[msg.sender] = INITIAL_SUPPLY;
    }

    function send(address to, uint256 amount) public {
        require(to != address(0));
        require(balances[msg.sender] >= amount);
        require(balances[to] + amount > balances[to]);

        balances[msg.sender] -= amount;
        balances[to] += amount;
    }

    function checkBalance(address account) public view returns (uint256) {
        return balances[account];
    }
}

部署脚本：2_deploy_token.js

var CryptoToken = artifacts.require("./CryptoToken.sol");

module.exports = function(deployer) {
  deployer.deploy(CryptoToken);
};

5. 前端集成

项目初始化：

npm init -y
npm install lite-server

配置文件：bs-config.json

{
    "server": {
        "baseDir": ["./src", "./build/contracts"]
    }
}

启动命令：

npm run dev