Hardhat v3: The Development Environment

import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox-viem";

const config: HardhatUserConfig = {
  solidity: "0.8.20",
};

export default config;

$ npx hardhat compile
Compiling 1 Solidity file
Generating typings for: 1 artifacts in dir: typechain-types
Successfully generated 6 typings!
Compilation finished successfully

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "hardhat/console.sol";

contract MyContract {
    uint256 public value;

    function setValue(uint256 _value) external {
        console.log("Old value: %s", value);
        console.log("New value: %s", _value);
        console.log("Caller: %s", msg.sender);
        value = _value;
    }
}

// Terminal output during test:
// Old value: 0
// New value: 42
// Caller: 0xf39Fd6e51...

import { loadFixture } from "@nomicfoundation/hardhat-toolbox-viem/network-helpers";
import { expect } from "chai";
import hre from "hardhat";

describe("MyToken", function () {
  async function deployFixture() {
    const [owner, alice, bob] = await hre.viem.getWalletClients();
    const token = await hre.viem.deployContract("MyToken", [
      "MyToken", "MTK", 1000000n
    ]);
    const publicClient = await hre.viem.getPublicClient();
    return { token, owner, alice, bob, publicClient };
  }

  it("should have correct name and symbol", async function () {
    const { token } = await loadFixture(deployFixture);
    expect(await token.read.name()).to.equal("MyToken");
    expect(await token.read.symbol()).to.equal("MTK");
  });

  it("should transfer tokens", async function () {
    const { token, owner, alice } = await loadFixture(deployFixture);
    await token.write.transfer([alice.account.address, 100n]);
    const balance = await token.read.balanceOf([alice.account.address]);
    expect(balance).to.equal(100n);
  });

  it("should revert on insufficient balance", async function () {
    const { token, alice, bob } = await loadFixture(deployFixture);
    await expect(
      token.write.transfer([bob.account.address, 100n],
        { account: alice.account })
    ).to.be.rejected;
  });
});

// ignition/modules/MyToken.ts
import { buildModule } from "@nomicfoundation/hardhat-ignition/modules";

const MyTokenModule = buildModule("MyTokenModule", (m) => {
  const token = m.contract("MyToken", ["MyToken", "MTK", 1_000_000n]);
  return { token };
});

export default MyTokenModule;

// Deploy command:
// npx hardhat ignition deploy ignition/modules/MyToken.ts --network localhost

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "hardhat/console.sol";

contract MyToken {
    mapping(address => uint256) private _balances;

    function transfer(address to, uint256 amount) external {
        console.log("Sender: %s, Balance: %s", msg.sender, _balances[msg.sender]);
        console.log("Transfer amount: %s to %s", amount, to);
        require(_balances[msg.sender] >= amount, "Insufficient balance");
        _balances[msg.sender] -= amount;
        _balances[to] += amount;
        console.log("Transfer complete. New balances:");
        console.log("  Sender: %s", _balances[msg.sender]);
        console.log("  Recipient: %s", _balances[to]);
    }
}