Instance of web3 with provider from web3 injected by MetaMask

web3.js

import Web3 from 'web3';
// We are assumming that the user has installed the Metamask browser extension
// and we are using Provider from the injected instance of web3
// to create instance of Web3 of our desired version
// See https://www.udemy.com/ethereum-and-solidity-the-complete-developers-guide/learn/v4/t/lecture/9020582?start=0 for more details
// This way we can simply import preconfigured instance of web3
const web3 = new Web3(window.web3.currentProvider);
export default web3;