alexroan

const Web3 = require("web3");

window.web3 = new Web3(window.ethereum);
window.ethereum.enable();

alexroan

import MyContract from "./contracts/MyContract.json";

const networkId = await web3.eth.net.getId();
const deployedNetwork = MyContract.networks[networkId];
const myContract = new web3.eth.Contract(
    MyContract.abi,
    deployedNetwork && deployedNetwork.address,
);

alexroan

const accounts = await web3.eth.getAccounts();
const account = accounts[0];

alexroan

myContract.events.MyEvent({})
    .on('data', async function(event){
        console.log(event.returnValues);
        // Do something here
    })
    .on('error', console.error);

alexroan

pragma solidity ^0.5.5;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Detailed.sol";

contract MyERC20 is ERC20, ERC20Detailed {
  constructor(string memory _name, string memory _symbol, uint8 _decimals) public ERC20Detailed(_name, _symbol, _decimals) {
  
  }
}

alexroan

pragma solidity ^0.5.5;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyERC721 is ERC721 {

	struct Person {
		string name;
		uint8 age;
		uint8 height;

alexroan

pragma solidity ^0.5.5;

import "@openzeppelin/contracts/math/SafeMath.sol";

contract BasicSafeMath {

  using SafeMath for uint;
  
  function doSomeMath(uint _a, uint _b) public returns (uint) {
    return _a.sub(_b);

alexroan

pragma solidity ^0.5.5;

import "@openzeppelin/contracts/math/SafeCast.sol";

contract BasicSafeCast {

  using SafeCast for uint;
  
  function castToUint8(uint _a) public returns (uint8) {
    return _a.toUint8();

alexroan

pragma solidity ^0.5.5;

import "@openzeppelin/contracts/ownership/Ownable.sol";

contract OwnableContract is Ownable {

  function restrictedFunction() public onlyOwner returns (uint) {
    return 99;
  }

alexroan

async function getAccount() {
  const accounts = await ethereum.enable();
  const account = accounts[0];
  // do something with new account here
}

ethereum.on('accountsChanged', function (accounts) {
  getAccount();
})