全栈智能合约（四）-react部分

react

App.js

import logo from './logo.svg';
import './App.css';
import React, {useState} from 'react'
import {ethers} from 'ethers'
import Greeter from './artifacts/contracts/Greeter.sol/Greeter.json'

const greeterAddress = '0x5FbDB2315678afecb367f032d93F642f64180aa3'

function App() {

  const [greeting, setGreetingValue] = useState("")

async function fetchGreeting(){
   
  if(typeof window.ethereum !== 'undefined'){
    // access metamask client 
    const provider = new ethers.providers.Web3Provider(window.ethereum)

    // create new instance of ethereum 
    const contract = new ethers.Contract(greeterAddress, Greeter.abi, provider)
    
    try{
      const data = await contract.greet()
      setGreetingValue(data)
      console.log('data:s', data)
    } catch(err){
      console.log('Error: ', err)
    }

  }

}

async function setGreeting(value){
 
  if(!value) return;
   
  if(!typeof window.ethereum !== 'undefined'){
    await requestAccount()
    const provider = new ethers.providers.Web3Provider(window.ethereum)
    const signer = provider.getSigner()
    const contract = new ethers.Contract(greeterAddress, Greeter.abi, provider)
    const transaction = await contract.setGreetingValue(value)
    await transaction.wait()
    fetchGreeting()
  }
}

async function requestAccount(){
  await window.ethereum.request({ method: 'eth_requestAccounts'})
}

async function handleSubmit(event){
  event.preventDefault()
  await setGreeting(event.target.greetingInput.value)
  setGreetingValue(event.target.greetingInput.value)
  event.target.greetingInput.value = ""
}

  
return (
  <div className="w-full max-w-lg container">
    <div className="shadow-md rounded px-8 pt-6 pb-8 mb-4 mt-4">
      React ethereum Dapp
    </div>
    <div className="w-full border-4 p-2 mb-4 rounded border-gary-400">
      <div className="text-gary-600 font-bold text-md mb-2">
        Fetch Greeting Message From Smart Contract
      </div>
      <div className="flex">
      <button className="bg-blue-500 hover:gb-blue-700 text-white"> Fetch Greeting </button>
    </div>
    </div>
    
    <div className="w-full border-4 p-2 mb-4 rounded border-gary-400">
      <div className="text-gary-600 font-bold text-md mb-2">
        Set Greeting Message On Smart Contract
      </div>
      <form className="flex items-center justify-between"
        onSubmit={event=>handleSubmit(event)}>
       <input className="shadow appearance-none border rounded py-2  px-3 text-gray-700 leading-tight focus:outline-none focus:shadow-outline"
        name= "greetingInput" />
       <button className="bg-red-500 hover:bg-blue-700 text-white font-bold py-2 px-4 rounded">
         Set Greeting
       </button>
 
      </form>

    </div>
    <div className="w-full border-4 p-2 mb-4 rounded border-gary-400">
        <div className="text-gary-600 font-bold text-md mb-2">
          Greeting Message
        </div>
        <p>
          {greeting}
        </p>

      </div>

  </div>
);
}


export default App;

运行 

npm start

编译完成

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