I have completed the CryptoZombies's chapter6 tutorial, so I am challenged to work the front in my environment.

When I try to connect to the contract from the frontend I get an error message.

var cryptoZombies;
var userAccount;

function startApp() {
    var cryptoZombiesAddress = "0x8b87e80e2b76b4445a869b3dd0640e37c51def50";
    cryptoZombies = new web3js.eth.Contract(cryptoZombiesABI, cryptoZombiesAddress);
    async function getCurrentAccount(){
      const web3 = new Web3(window.ethereum);
      const userAccount = await web3.eth.getAccounts();
      return userAccount;

function displayZombies(ids) {
    for (id of ids) {
      // Look up zombie details from our contract. Returns a `zombie` object
      .then(function(zombie) {
        // Using ES6's "template literals" to inject variables into the HTML.
        // Append each one to our #zombies div
        $("#zombies").append(`<div class="zombie">
            <li>Name: ${zombie.name}</li>
            <li>DNA: ${zombie.dna}</li>
            <li>Level: ${zombie.level}</li>
            <li>Wins: ${zombie.winCount}</li>
            <li>Losses: ${zombie.lossCount}</li>
            <li>Ready Time: ${zombie.readyTime}</li>

function getZombiesByOwner(owner) {
    return cryptoZombies.methods.getZombiesByOwner(owner).call();

window.addEventListener('load', function() {
    // Checking if Web3 has been injected by the browser (Mist/MetaMask)
    if (typeof web3 !== 'undefined') {
      // Use Mist/MetaMask's provider
      web3js = new Web3(window.ethereum);
    } else {
      // Handle the case where the user doesn't have Metamask installed
      // Probably show them a message prompting them to install Metamask
      alert("please install metamask");
    // Now you can start your app & access web3 freely:

I can get the current metamask account. However, When I try to run


it return an error.

invalid address (argument="address", value=undefined, code=INVALID_ARGUMENT, version=address/5.5.0) (argument="_owner", value=undefined, code=INVALID_ARGUMENT, version=abi/5.0.7)

1 Answer 1


You need to use a checksummed address.

Web3 has a function that does that -

    var cryptoZombiesAddress = "0x8b87e80e2b76b4445a869b3dd0640e37c51def50";
    cryptoZombies = new web3js.eth.Contract(cryptoZombiesABI, web3js.utils.toChecksumAddress(cryptoZombiesAddress));

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.