• node: 16.13.1
• npm: 8.1.2

A wei is the smallest sub-unit of Ether — there are 10^18 wei in one ether.

msg.sender

In order to filter events and only listen for changes related to the current user, Solidity contract would have to use the indexed keyword, like we did in the Transfer event of our ERC721 implementation:

event Transfer(address indexed _from, address indexed_to, uint256 _tokenId);

// Use `filter` to only fire this code when `_to` equals `userAccount`
cryptoZombies.events.Transfer({ filter: { _to: userAccount } })
    .on("data", function(event) {
        let data = event.returnValues;
        // The current user just received a zombie!
        // Do something here to update the UI to show it
    })
    .on("error", console.error);

We can even query past events using getPastEvents, and use the filters fromBlock and toBlock to give Solidity a time range for the event logs ("block" in this case referring to the Ethereum block number):

cryptoZombies.getPastEvents("NewZombie", { fromBlock: 0, toBlock: "latest" })
    .then(function(events) {
    // `events` is an array of `event` objects that we can iterate, like we did above
    // This code will get us a list of every zombie that was ever created
    });

This project demonstrates an advanced Hardhat use case, integrating other tools commonly used alongside Hardhat in the ecosystem.

The project comes with a sample contract, a test for that contract, a sample script that deploys that contract, and an example of a task implementation, which simply lists the available accounts. It also comes with a variety of other tools, preconfigured to work with the project code.

Try running some of the following tasks:

npx hardhat accounts
npx hardhat compile
npx hardhat clean
npx hardhat test
npx hardhat node
npx hardhat help
REPORT_GAS=true npx hardhat test
npx hardhat coverage
npx hardhat run scripts/deploy.ts
TS_NODE_FILES=true npx ts-node scripts/deploy.ts
npx eslint '**/*.{js,ts}'
npx eslint '**/*.{js,ts}' --fix
npx prettier '**/*.{json,sol,md}' --check
npx prettier '**/*.{json,sol,md}' --write
npx solhint 'contracts/**/*.sol'
npx solhint 'contracts/**/*.sol' --fix

npx webpack
cd dist
python -m http.server 6969

npx hardhat node
npx hardhat run scripts/deploy.ts --network localhost

cat artifacts/contracts/Hero.sol/Hero.json | jq .deployedBytecode 

To try out Etherscan verification, you first need to deploy a contract to an Ethereum network that's supported by Etherscan, such as Ropsten.

In this project, copy the .env.example file to a file named .env, and then edit it to fill in the details. Enter your Etherscan API key, your Ropsten node URL (eg from Alchemy), and the private key of the account which will send the deployment transaction. With a valid .env file in place, first deploy your contract:

hardhat run --network ropsten scripts/sample-script.ts

Then, copy the deployment address and paste it in to replace DEPLOYED_CONTRACT_ADDRESS in this command:

npx hardhat verify --network ropsten DEPLOYED_CONTRACT_ADDRESS "Hello, Hardhat!"

For faster runs of your tests and scripts, consider skipping ts-node's type checking by setting the environment variable TS_NODE_TRANSPILE_ONLY to 1 in hardhat's environment. For more details see the documentation.