web3.js

import Web3 from 'web3';

const web3 = new Web3(window.web3.currentProvider);

window.addEventListener('load', async () => {
    // Modern dapp browsers...
    if (window.ethereum) {
        window.web3 = new Web3(ethereum);
        try {
            // Request account access if needed
            await ethereum.enable();
            // Acccounts now exposed
            web3.eth.sendTransaction({/* ... */});
        } catch (error) {
            // User denied account access...
        }
    }
    // Legacy dapp browsers...
    else if (window.web3) {
        window.web3 = new Web3(web3.currentProvider);
        // Acccounts always exposed
        web3.eth.sendTransaction({/* ... */});
    }
    // Non-dapp browsers...
    else {
        console.log('Non-Ethereum browser detected. You should consider trying MetaMask!');
    }
});

//https://medium.com/metamask/https-medium-com-metamask-breaking-change-injecting-web3-7722797916a8
export default web3;