ether.js と React を使用して DApps を開発します。

ether.js の npm パッケージ名は ethers なので、それをインストールします。

Truffleを使ったスマートコントラクト開発 で Counter スマートコントラクトを build すると Counter スマートコントラクトの情報(ABIやaddressなど)が truffle_project\build\contracts\Counter.json に保存されています。今回はその Counter.json を react-etherjs\src\contracts\Counter.json にコピーして使用します。

本来は truffle-config.js の設定を変更して、Counter.json を react-etherjs\src\contracts に保存するようにするのが一般的です。

react-etherjs> mkdir .\src\contracts
 
 
    ディレクトリ: C:\Users\miyazato\work\ethereum\react-etherjs\src
 
 
Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----        2022/05/08     20:50                contracts
 
 
react-etherjs> cp ..\contracts\Counter.sol .\src\contracts\.

import './App.css';
 
import React, {  useState } from "react";
import { ethers } from "ethers";
 
function App() {
  const [provider, setProvider] = useState(null);
  const [counter, setCounter] = useState(null);
  const [account, setAccount] = useState();
  const [count, setCount] = useState();
  const [transactionHash, setTransactionHash] = useState();
  const [transactionInfo, setTransactionInfo] = useState();
 
  const counterAddress = "0x5E5A16AaFb816F04E09a05d1C03d98D7b1ee56C2";
  const counterAbi = [
        {
        "constant": true,
        "inputs": [],
        "name": "count",
        "outputs": [
            {
            "internalType": "uint256",
            "name": "",
            "type": "uint256"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
        },
        {
        "constant": true,
        "inputs": [],
        "name": "get",
        "outputs": [
            {
            "internalType": "uint256",
            "name": "",
            "type": "uint256"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
        },
        {
        "constant": false,
        "inputs": [],
        "name": "inc",
        "outputs": [],
        "payable": false,
        "stateMutability": "nonpayable",
        "type": "function"
        },
        {
        "constant": false,
        "inputs": [],
        "name": "dec",
        "outputs": [],
        "payable": false,
        "stateMutability": "nonpayable",
        "type": "function"
        }
    ];
 
    //メタマスクの接続
    const connectMetaMask= () => {
        if (window.ethereum && window.ethereum.isMetaMask) {
            window.ethereum
                .request({ method: "eth_requestAccounts" })
                .then((result) => {
                    setAccount(result[0]);
                    let provider = new ethers.providers.Web3Provider(window.ethereum);
                    let signer = provider.getSigner(0);
                    setCounter(new ethers.Contract(counterAddress, counterAbi, signer));
                    setProvider(provider);
                })
                .catch((error) => {
                    console.log("MetaMask error" + error)
                });
        } else {
            console.log("Need to install MetaMask");
        }
    };
 
  // Counter.get でカウントの値を取得する関数
  const  getCount =  async () => {
    let count = await counter.get();
    setCount(count.toNumber());
  };
 
  // Counter.inc を呼び出す関数
  const  incCount =  async () => {
    let transaction = await counter.inc();
    await transaction.wait();
    setTransactionHash(transaction.hash);
    getCount();
  };
 
  // Counterdec を呼び出す関数
  const  decCount =  async () => {
    let transaction = await counter.dec();
    await transaction.wait();
    setTransactionHash(transaction.hash);
    getCount();
  };
 
  // transactionHash からトランザクション情報を取得する関数
  const getTransactionInfo =  async () => {
    let transactionInfo = await provider.getTransaction(transactionHash);
    setTransactionInfo(JSON.stringify(transactionInfo, null, 2));
  };
 
  return (
    <div className="App">
      <header className="App-header">
      <div>
        Account: { account }
        <div>
            Count: { count }
        </div>
        <div>
            TransactionHash: { transactionHash }
        </div>
        <input type="button" value="connect" onClick={ connectMetaMask }/>
        <input type="button" value="get" onClick={ getCount }/>
        <input type="button" value="inc" onClick={ incCount }/>
        <input type="button" value="dec" onClick={ decCount }/>
        <input type="button" value="getTransactionInfo" onClick={ getTransactionInfo } />
      </div>
      <div>
        <pre>
          { transactionInfo }
        </pre>
      </div>
      </header>
    </div>
  );
}
 
export default App;