getWeb3.js

const getWeb3 = () => {
  return new Promise((resolve, reject) => {
    window.addEventListener("load", async () => {
      if (window.ethereum) {
        const web3 = new Web3(window.ethereum);
        try {
          // ask user permission to access his accounts
          await window.ethereum.request({ method: "eth_requestAccounts" });
          resolve(web3);
        } catch (error) {
          reject(error);
        }
      } else {
        reject("Must install MetaMask");
      }
    });
  });
};