web3-ethclient.js

// starting up a dapp
window.addEventListener('load', async () => {
    if (window.ethereum) { // Modern dapp browsers... 
        window.web3 = new Web3(ethereum);
        try {
            await ethereum.enable(); // Request account access if needed
        } catch (error) {
            console.log('User denied permission to use their Ethereum account.');
        }
    } else if (window.web3) { // Legacy dapp browsers...
        window.web3 = new Web3(web3.currentProvider);
    } else { // Non-dapp browsers...
        console.log('Non-Ethereum browser detected. You should consider trying MetaMask!');
    }
});