React js：./src/App.js第22行：未定义'lastWinner'no-undef搜索关键字以了解有关每个错误的更多信息

Question

Hello all I'm learning the basics of react, and how to program in solidity. I recently completed this smart contract that functions as a lottery and have full functionality. I have gone back and now want to display the address of the winner who will receive the funds from the lottery but have encountered this error

./src/App.js Line 22: 'lastWinner' is not defined no-undef

Search for the keywords to learn more about each error.

Here is the main react component *note- have have starred/ bolded the area where the error is

import React, { Component } from 'react';
//import logo from './logo.svg';
import './App.css';
import web3 from './web3';
import lottery from './lottery';

class App extends Component {
    state ={
      manager: ' ',
      players: [] , // players set to empty array
      balance: ' ',
      value: ' ',
      message: ' ',
      **lastWinner:' ',**
  }; //inatilizing state

  async componentDidMount() {
    const manager = await lottery.methods.manager().call();// retrieve manager from ETH ntwrk
    const winner = await lottery.methods.pickWinner().call(); // displays last winner address
    const players = await lottery.methods.getPlayer().call(); // get number of players
    const balance = await web3.eth.getBalance(lottery.options.address); // get contract's balance
    this.setState({manager, players, balance, **lastWinner**});// set state object
    }

    onSubmit= async (event) => { // function that calls contract entry
      event.preventDefault(); //makes sure form doesnt auto submit itself
      const accounts = await web3.eth.getAccounts(); // get accounts enterd in lotto
      this.setState({message: 'Waiting on transaction to be processed'}); //tells users whats going on with application
      //asume 1st account in array is entering lotto
      await lottery.methods.enter().send({
        from: accounts [0],
        value: web3.utils.toWei(this.state.value, 'ether')

      });
      this.setState({message: 'You have been entered'}); // update message
    };

    onClick = async () => {
      const accounts = await web3.eth.getAccounts(); // get accounts enterd in lotto
      this.setState({message: 'Waiting on transaction to be processed'});
      await lottery.methods.pickWinner().send({ // calls picks winner function
        from: accounts[0]
      });
      this.setState({message: 'Winner has been picked'});
    };
  render() {



    return (
      <div>
        <h2>Lottery Contract</h2>
        <p>
        This contract is managed by {this.state.manager}.
        Currently {this.state.players.length} people entered in the lottery.
        The lottery is valued at {web3.utils.fromWei(this.state.balance, 'ether')} ether!
          The last person to win was: {this.state.lastWinner}.
        </p>

        <hr/>

        <form onSubmit ={this.onSubmit}>
          <h4>Want to try your luck?</h4>
            <div>
              <label>Amount of ETH to enter. </label>
                <input
                value = {this.state.value}
                onChange={event => this.setState({value: event.target.value })} // updates a prop. called value which hold amount of ether

                />
            </div>
              <button>Enter</button>
        </form>

        <hr/>
          <h4>Ready to Pick a winner?</h4>
          <button onClick={this.onClick}> Pick~Winner</button>
        <hr/>
        <h1>{this.state.message}</h1>
      </div>
    );
  }
}

export default App;

also here is my code for the Ethereum Contract

pragma solidity  ^0.4.17;

contract Lottery{
  address public manager;
  address[] public players;
  address public lastWinner;

function Lottery() public{ // starting of lottery creation contract. assigns the person who calls this contract as manager.
  manager = msg.sender;
}

function enter() public payable { // entry function to contract- requires that entrants must submit at lesat .01ETH
  require(msg.value  > 0.01 ether);

  players.push(msg.sender);
}

function random() private view returns (uint){ // function that CALCULATES a winner based on current block diff. present time, and # of players
  return uint(keccak256(block.difficulty, now, players));//note* ispsudo random, can be reverse engineered.
}

function pickWinner() public restricted{ //inclusion of function modifier named 'restricted'
  //require (msg.sender == manager);  --Including the function modifier 'restriced' reduces the need for this duplicate line

  uint index = random() % players.length; //uses random calculation and modulods op to calculate a winner from index of players
  players[index].transfer(this.balance); //sends lottery funds to the index positioned winner
  players = new address[](0); // resets players in contract index back to 0
  lastWinner = players[index]; // records address of person who last won lottery
  lastWinner = msg.sender;
  //return lastWinner;
}

modifier restricted(){ // function modifier- purpose to reduce the need for repetitive code. can be applied on any function
  require (msg.sender == manager);
  _;
}

function getPlayer()public view returns(address[]){ //function that returns the full list of players entered into the lottery
  return players;  // public- seen by everyone~ view- does not modify contract data~ should return a dynamic array of addys.
}

}

Answer 1

In the line:

this.setState({manager, players, balance, **lastWinner**});// set state object

You are trying to pass in a variable called lastWinner but the variable you defined for the winner is called winner :

const winner = await lottery.methods.pickWinner().call(); // displays last winner address

Either change the variable name to lastWinner:

const lastWinner = await lottery.methods.pickWinner().call(); // displays last winner address

Or pass in the winner variable with the lastWinner key:

this.setState({manager, players, balance, lastWinner: winner});