Crypto-DAPP-UseEffect final.js

  // this will trigger whenever the App function is called, which index.js runs at startup
  useEffect(() => {
    // Here we check if there is web3 support
    if (typeof web3 !== 'undefined') {
      window.web3 = new Web3(window.web3.currentProvider)
      // Check if its MetaMask that is installed
      if (window.web3.currentProvider.isMetaMask === true) {
        connectMetaMask();
        connectToSelectedNetwork();
      } else {
        // Another web3 provider, add support if you want
      }
    }else {
      // The browser has no web3 
      // Suggest the user to install a web3 compatible browser plugin
      throw new Error("No web3 support, redirect user to a download page or something :) ");
    }
  }, []);