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# Overview

Hardhat is a development environment for Ethereum software. It consists of different components for editing, compiling, debugging and deploying your smart contracts and dApps, all of which work together to create a complete development environment.

Hardhat Runner is the main component you interact with when using Hardhat. It's a flexible and extensible task runner that helps you manage and automate the recurring tasks inherent to developing smart contracts and dApps.

Hardhat Runner is designed around the concepts of tasks and plugins. Every time you're running Hardhat from the command-line, you're running a task. For example, npx hardhat compile runs the built-in compile task. Tasks can call other tasks, allowing complex workflows to be defined. Users and plugins can override existing tasks, making those workflows customizable and extendable.

This guide will take you through the installation of our recommended setup, but as most of Hardhat's functionality comes from plugins, you are free to customize it or choose a completely different path.

# Installation

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Hardhat for Visual Studio Code is the official Hardhat extension that adds advanced support for Solidity to VSCode. If you use Visual Studio Code, give it a try!

Hardhat is used through a local installation in your project. This way your environment will be reproducible, and you will avoid future version conflicts.

To install it, you need to create an npm project by going to an empty folder, running npm init, and following its instructions. You can use another package manager, like yarn, but we recommend you use npm 7 or later, as it makes installing Hardhat plugins simpler.

Once your project is ready, you should run

npm 7+
npm 6
yarn
npm install --save-dev hardhat
npm install --save-dev hardhat
yarn add --dev hardhat

To use your local installation of Hardhat, you need to use npx to run it (i.e. npx hardhat init).

# Quick Start

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If you are using Windows, we strongly recommend using WSL 2 to follow this guide.

We will explore the basics of creating a Hardhat project with a sample contract, tests of that contract, and a script to deploy it.

To create the sample project, run npx hardhat init in your project folder:

$ npx hardhat init
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8888888888  8888b.  888d888 .d88888 88888b.   8888b.  888888
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888    888 .d888888 888    888  888 888  888 .d888888 888
888    888 888  888 888    Y88b 888 888  888 888  888 Y88b.
888    888 "Y888888 888     "Y88888 888  888 "Y888888  "Y888

πŸ‘· Welcome to Hardhat v2.19.2 πŸ‘·β€

? What do you want to do? …
❯ Create a JavaScript project
  Create a TypeScript project
  Create a TypeScript project (with Viem)
  Create an empty hardhat.config.js
  Quit

Let’s create the JavaScript or TypeScript project and go through these steps to compile, test and deploy the sample contract. We recommend using TypeScript, but if you are not familiar with it just pick JavaScript.

#Running tasks

To first get a quick sense of what's available and what's going on, run npx hardhat in your project folder:

$ npx hardhat
Hardhat version 2.9.9

Usage: hardhat [GLOBAL OPTIONS] <TASK> [TASK OPTIONS]

GLOBAL OPTIONS:

  --config              A Hardhat config file.
  --emoji               Use emoji in messages.
  --help                Shows this message, or a task's help if its name is provided
  --max-memory          The maximum amount of memory that Hardhat can use.
  --network             The network to connect to.
  --show-stack-traces   Show stack traces.
  --tsconfig            A TypeScript config file.
  --verbose             Enables Hardhat verbose logging
  --version             Shows hardhat's version.


AVAILABLE TASKS:

  check                 Check whatever you need
  clean                 Clears the cache and deletes all artifacts
  compile               Compiles the entire project, building all artifacts
  console               Opens a hardhat console
  coverage              Generates a code coverage report for tests
  flatten               Flattens and prints contracts and their dependencies
  help                  Prints this message
  node                  Starts a JSON-RPC server on top of Hardhat Network
  run                   Runs a user-defined script after compiling the project
  test                  Runs mocha tests
  typechain             Generate Typechain typings for compiled contracts
  verify                Verifies contract on Etherscan

To get help for a specific task run: npx hardhat help [task]

The list of available tasks includes the built-in ones and also those that came with any installed plugins. npx hardhat is your starting point to find out what tasks are available to run.

#Compiling your contracts

Next, if you take a look in the contracts/ folder, you'll see Lock.sol:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.9;

// Uncomment this line to use console.log
// import "hardhat/console.sol";

contract Lock {
    uint public unlockTime;
    address payable public owner;

    event Withdrawal(uint amount, uint when);

    constructor(uint _unlockTime) payable {
        require(
            block.timestamp < _unlockTime,
            "Unlock time should be in the future"
        );

        unlockTime = _unlockTime;
        owner = payable(msg.sender);
    }

    function withdraw() public {
        // Uncomment this line, and the import of "hardhat/console.sol", to print a log in your terminal
        // console.log("Unlock time is %o and block timestamp is %o", unlockTime, block.timestamp);

        require(block.timestamp >= unlockTime, "You can't withdraw yet");
        require(msg.sender == owner, "You aren't the owner");

        emit Withdrawal(address(this).balance, block.timestamp);

        owner.transfer(address(this).balance);
    }
}

To compile it, simply run:

npx hardhat compile

If you created a TypeScript project, this task will also generate TypeScript bindings using TypeChain.

#Testing your contracts

Your project comes with tests that use Mocha, Chai, and Ethers.js.

If you take a look in the test/ folder, you'll see a test file:

TypeScript
JavaScript
import {
  time,
  loadFixture,
} from "@nomicfoundation/hardhat-toolbox/network-helpers";
import { anyValue } from "@nomicfoundation/hardhat-chai-matchers/withArgs";
import { expect } from "chai";
import { ethers } from "hardhat";

describe("Lock", function () {
  // We define a fixture to reuse the same setup in every test.
  // We use loadFixture to run this setup once, snapshot that state,
  // and reset Hardhat Network to that snapshot in every test.
  async function deployOneYearLockFixture() {
    const ONE_YEAR_IN_SECS = 365 * 24 * 60 * 60;
    const ONE_GWEI = 1_000_000_000;

    const lockedAmount = ONE_GWEI;
    const unlockTime = (await time.latest()) + ONE_YEAR_IN_SECS;

    // Contracts are deployed using the first signer/account by default
    const [owner, otherAccount] = await ethers.getSigners();

    const Lock = await ethers.getContractFactory("Lock");
    const lock = await Lock.deploy(unlockTime, { value: lockedAmount });

    return { lock, unlockTime, lockedAmount, owner, otherAccount };
  }

  describe("Deployment", function () {
    it("Should set the right unlockTime", async function () {
      const { lock, unlockTime } = await loadFixture(deployOneYearLockFixture);

      expect(await lock.unlockTime()).to.equal(unlockTime);
    });

    it("Should set the right owner", async function () {
      const { lock, owner } = await loadFixture(deployOneYearLockFixture);

      expect(await lock.owner()).to.equal(owner.address);
    });

    it("Should receive and store the funds to lock", async function () {
      const { lock, lockedAmount } = await loadFixture(
        deployOneYearLockFixture
      );

      expect(await ethers.provider.getBalance(lock.target)).to.equal(
        lockedAmount
      );
    });

    it("Should fail if the unlockTime is not in the future", async function () {
      // We don't use the fixture here because we want a different deployment
      const latestTime = await time.latest();
      const Lock = await ethers.getContractFactory("Lock");
      await expect(Lock.deploy(latestTime, { value: 1 })).to.be.revertedWith(
        "Unlock time should be in the future"
      );
    });
  });

  describe("Withdrawals", function () {
    describe("Validations", function () {
      it("Should revert with the right error if called too soon", async function () {
        const { lock } = await loadFixture(deployOneYearLockFixture);

        await expect(lock.withdraw()).to.be.revertedWith(
          "You can't withdraw yet"
        );
      });

      it("Should revert with the right error if called from another account", async function () {
        const { lock, unlockTime, otherAccount } = await loadFixture(
          deployOneYearLockFixture
        );

        // We can increase the time in Hardhat Network
        await time.increaseTo(unlockTime);

        // We use lock.connect() to send a transaction from another account
        await expect(lock.connect(otherAccount).withdraw()).to.be.revertedWith(
          "You aren't the owner"
        );
      });

      it("Shouldn't fail if the unlockTime has arrived and the owner calls it", async function () {
        const { lock, unlockTime } = await loadFixture(
          deployOneYearLockFixture
        );

        // Transactions are sent using the first signer by default
        await time.increaseTo(unlockTime);

        await expect(lock.withdraw()).not.to.be.reverted;
      });
    });

    describe("Events", function () {
      it("Should emit an event on withdrawals", async function () {
        const { lock, unlockTime, lockedAmount } = await loadFixture(
          deployOneYearLockFixture
        );

        await time.increaseTo(unlockTime);

        await expect(lock.withdraw())
          .to.emit(lock, "Withdrawal")
          .withArgs(lockedAmount, anyValue); // We accept any value as `when` arg
      });
    });

    describe("Transfers", function () {
      it("Should transfer the funds to the owner", async function () {
        const { lock, unlockTime, lockedAmount, owner } = await loadFixture(
          deployOneYearLockFixture
        );

        await time.increaseTo(unlockTime);

        await expect(lock.withdraw()).to.changeEtherBalances(
          [owner, lock],
          [lockedAmount, -lockedAmount]
        );
      });
    });
  });
});

const {
  time,
  loadFixture,
} = require("@nomicfoundation/hardhat-toolbox/network-helpers");
const { anyValue } = require("@nomicfoundation/hardhat-chai-matchers/withArgs");
const { expect } = require("chai");

describe("Lock", function () {
  // We define a fixture to reuse the same setup in every test.
  // We use loadFixture to run this setup once, snapshot that state,
  // and reset Hardhat Network to that snapshot in every test.
  async function deployOneYearLockFixture() {
    const ONE_YEAR_IN_SECS = 365 * 24 * 60 * 60;
    const ONE_GWEI = 1_000_000_000;

    const lockedAmount = ONE_GWEI;
    const unlockTime = (await time.latest()) + ONE_YEAR_IN_SECS;

    // Contracts are deployed using the first signer/account by default
    const [owner, otherAccount] = await ethers.getSigners();

    const Lock = await ethers.getContractFactory("Lock");
    const lock = await Lock.deploy(unlockTime, { value: lockedAmount });

    return { lock, unlockTime, lockedAmount, owner, otherAccount };
  }

  describe("Deployment", function () {
    it("Should set the right unlockTime", async function () {
      const { lock, unlockTime } = await loadFixture(deployOneYearLockFixture);

      expect(await lock.unlockTime()).to.equal(unlockTime);
    });

    it("Should set the right owner", async function () {
      const { lock, owner } = await loadFixture(deployOneYearLockFixture);

      expect(await lock.owner()).to.equal(owner.address);
    });

    it("Should receive and store the funds to lock", async function () {
      const { lock, lockedAmount } = await loadFixture(
        deployOneYearLockFixture
      );

      expect(await ethers.provider.getBalance(lock.target)).to.equal(
        lockedAmount
      );
    });

    it("Should fail if the unlockTime is not in the future", async function () {
      // We don't use the fixture here because we want a different deployment
      const latestTime = await time.latest();
      const Lock = await ethers.getContractFactory("Lock");
      await expect(Lock.deploy(latestTime, { value: 1 })).to.be.revertedWith(
        "Unlock time should be in the future"
      );
    });
  });

  describe("Withdrawals", function () {
    describe("Validations", function () {
      it("Should revert with the right error if called too soon", async function () {
        const { lock } = await loadFixture(deployOneYearLockFixture);

        await expect(lock.withdraw()).to.be.revertedWith(
          "You can't withdraw yet"
        );
      });

      it("Should revert with the right error if called from another account", async function () {
        const { lock, unlockTime, otherAccount } = await loadFixture(
          deployOneYearLockFixture
        );

        // We can increase the time in Hardhat Network
        await time.increaseTo(unlockTime);

        // We use lock.connect() to send a transaction from another account
        await expect(lock.connect(otherAccount).withdraw()).to.be.revertedWith(
          "You aren't the owner"
        );
      });

      it("Shouldn't fail if the unlockTime has arrived and the owner calls it", async function () {
        const { lock, unlockTime } = await loadFixture(
          deployOneYearLockFixture
        );

        // Transactions are sent using the first signer by default
        await time.increaseTo(unlockTime);

        await expect(lock.withdraw()).not.to.be.reverted;
      });
    });

    describe("Events", function () {
      it("Should emit an event on withdrawals", async function () {
        const { lock, unlockTime, lockedAmount } = await loadFixture(
          deployOneYearLockFixture
        );

        await time.increaseTo(unlockTime);

        await expect(lock.withdraw())
          .to.emit(lock, "Withdrawal")
          .withArgs(lockedAmount, anyValue); // We accept any value as `when` arg
      });
    });

    describe("Transfers", function () {
      it("Should transfer the funds to the owner", async function () {
        const { lock, unlockTime, lockedAmount, owner } = await loadFixture(
          deployOneYearLockFixture
        );

        await time.increaseTo(unlockTime);

        await expect(lock.withdraw()).to.changeEtherBalances(
          [owner, lock],
          [lockedAmount, -lockedAmount]
        );
      });
    });
  });
});

You can run your tests with npx hardhat test:

TypeScript
JavaScript
$ npx hardhat test
Generating typings for: 2 artifacts in dir: typechain-types for target: ethers-v6
Successfully generated 6 typings!
Compiled 2 Solidity files successfully


  Lock
    Deployment
      βœ” Should set the right unlockTime (610ms)
      βœ” Should set the right owner
      βœ” Should receive and store the funds to lock
      βœ” Should fail if the unlockTime is not in the future
    Withdrawals
      Validations
        βœ” Should revert with the right error if called too soon
        βœ” Should revert with the right error if called from another account
        βœ” Shouldn't fail if the unlockTime has arrived and the owner calls it
      Events
        βœ” Should emit an event on withdrawals
      Transfers
        βœ” Should transfer the funds to the owner


  9 passing (790ms)
$ npx hardhat test
Compiled 2 Solidity files successfully


  Lock
    Deployment
      βœ” Should set the right unlockTime (610ms)
      βœ” Should set the right owner
      βœ” Should receive and store the funds to lock
      βœ” Should fail if the unlockTime is not in the future
    Withdrawals
      Validations
        βœ” Should revert with the right error if called too soon
        βœ” Should revert with the right error if called from another account
        βœ” Shouldn't fail if the unlockTime has arrived and the owner calls it
      Events
        βœ” Should emit an event on withdrawals
      Transfers
        βœ” Should transfer the funds to the owner


  9 passing (790ms)

#Deploying your contracts

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Try Hardhat Ignition for your deployments! Our new declarative system for deploying smart contracts without getting caught up in execution details.

Next, to deploy the contract we will use a Hardhat script.

Inside the scripts/ folder you will find a file with the following code:

TypeScript
JavaScript
import { ethers } from "hardhat";

async function main() {
  const currentTimestampInSeconds = Math.round(Date.now() / 1000);
  const unlockTime = currentTimestampInSeconds + 60;

  const lockedAmount = ethers.parseEther("0.001");

  const lock = await ethers.deployContract("Lock", [unlockTime], {
    value: lockedAmount,
  });

  await lock.waitForDeployment();

  console.log(
    `Lock with ${ethers.formatEther(
      lockedAmount
    )}ETH and unlock timestamp ${unlockTime} deployed to ${lock.target}`
  );
}

// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

// We require the Hardhat Runtime Environment explicitly here. This is optional
// but useful for running the script in a standalone fashion through `node <script>`.
//
// You can also run a script with `npx hardhat run <script>`. If you do that, Hardhat
// will compile your contracts, add the Hardhat Runtime Environment's members to the
// global scope, and execute the script.
const hre = require("hardhat");

async function main() {
  const currentTimestampInSeconds = Math.round(Date.now() / 1000);
  const unlockTime = currentTimestampInSeconds + 60;

  const lockedAmount = hre.ethers.parseEther("0.001");

  const lock = await hre.ethers.deployContract("Lock", [unlockTime], {
    value: lockedAmount,
  });

  await lock.waitForDeployment();

  console.log(
    `Lock with ${ethers.formatEther(
      lockedAmount
    )}ETH and unlock timestamp ${unlockTime} deployed to ${lock.target}`
  );
}

// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

You can run it using npx hardhat run:

TypeScript
JavaScript
$ npx hardhat run scripts/deploy.ts
Lock with 1 ETH deployed to: 0x5FbDB2315678afecb367f032d93F642f64180aa3
$ npx hardhat run scripts/deploy.js
Lock with 1 ETH deployed to: 0x5FbDB2315678afecb367f032d93F642f64180aa3

#Connecting a wallet or Dapp to Hardhat Network

By default, Hardhat will spin up a new in-memory instance of Hardhat Network on startup. It's also possible to run Hardhat Network in a standalone fashion so that external clients can connect to it. This could be a wallet, your Dapp front-end, or a script.

To run Hardhat Network in this way, run npx hardhat node:

$ npx hardhat node
Started HTTP and WebSocket JSON-RPC server at http://127.0.0.1:8545/

This will expose a JSON-RPC interface to Hardhat Network. To use it connect your wallet or application to http://127.0.0.1:8545.

If you want to connect Hardhat to this node, for example to run a deployment script against it, you simply need to run it using --network localhost.

To try this, start a node with npx hardhat node and re-run the deployment script using the network option:

TypeScript
JavaScript
npx hardhat run scripts/deploy.ts --network localhost
npx hardhat run scripts/deploy.js --network localhost

Congrats! You have created a project and compiled, tested and deployed a smart contract.

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