Someone knows something about this error with Truffle React box? Must be my Metamask wallet address but it is already in my truffle-config file.

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I leave the App.js file here (I didn't make it. It's just the code of Truffle React Box). I've just followed the steps here: https://www.trufflesuite.com/boxes/react

import React, { Component } from "react";
import SimpleStorageContract from "./contracts/SimpleStorage.json";
import getWeb3 from "./getWeb3";

import "./App.css";

class App extends Component {
  state = { storageValue: 0, web3: null, accounts: null, contract: null };

  componentDidMount = async () => {
    try {
      // Get network provider and web3 instance.
      const web3 = await getWeb3();
      // Use web3 to get the user's accounts.
      const accounts = await web3.eth.getAccounts();

      // Get the contract instance.
      const networkId = await web3.eth.net.getId();
      const deployedNetwork = SimpleStorageContract.networks[networkId];
      const instance = new web3.eth.Contract(
        deployedNetwork && deployedNetwork.address,

      // Set web3, accounts, and contract to the state, and then proceed with an
      // example of interacting with the contract's methods.
      this.setState({ web3, accounts, contract: instance }, this.runExample);
    } catch (error) {
      // Catch any errors for any of the above operations.
        `Failed to load web3, accounts, or contract. Check console for details.`,

  runExample = async () => {
    const { accounts, contract } = this.state;

    // Stores a given value, 5 by default.
    await contract.methods.set(5).send({ from: accounts[0] });

    // Get the value from the contract to prove it worked.
    const response = await contract.methods.get().call();

    // Update state with the result.
    this.setState({ storageValue: response });

  render() {
    if (!this.state.web3) {
      return <div>Loading Web3, accounts, and contract...</div>;
    return (
      <div className="App">
        <h1>Good to Go!</h1>
        <p>Your Truffle Box is installed and ready.</p>
        <h2>Smart Contract Example</h2>
          If your contracts compiled and migrated successfully, below will show
          a stored value of 5 (by default).
          Try changing the value stored on <strong>line 42</strong> of App.js.
        <div>The stored value is: {this.state.storageValue}</div>

export default App;


After this piece of code:

      const instance = new web3.eth.Contract(
        deployedNetwork && deployedNetwork.address,

I've added this line:

instance.options.address = "[my contract' address on kovan]"

  • is truffle still used? I thought it was a relic
    – Nulik
    Jul 27, 2021 at 16:02
  • @Nulik is there another way to make your DApp "easily"? I'm just starting with DApps and there're lot of things to learn.
    – Joncarre
    Jul 27, 2021 at 16:14
  • many people use hardhat, check it out
    – Nulik
    Jul 27, 2021 at 16:23
  • I'll check it out but... I'd like to try with Truffle and work with React framework.
    – Joncarre
    Jul 27, 2021 at 21:46
  • 1
    Where do you "declare" the contract? Jul 29, 2021 at 5:36


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