Getting started

Hardhat is an Ethereum development environment, designed for easy smart contract development. One of its most prominent features is extendability: you can easily add new plugins to your hardhat project.

Along with the official plugins, there are other plugins from the community that you can use with ZKsync Era.

To learn more about Hardhat itself, check out the official documentation.

This tutorial shows you how to setup a ZKsync Era Solidity project with Hardhat using the ZKsync CLI.

If you are using Vyper, check out the Vyper plugin documentation or the vyper-example in GitHub!

Project setup

To create a new project run the zksync-cli create command, passing a project name:

Solidity project

npx zksync-cli create demo --template hardhat_solidity

Vyper project

npx zksync-cli create demo --template hardhat_vyper

This command creates a demo folder and clones a Hardhat template project inside it. The downloaded project is already configured and contains all the required plugins.

Hardhat configuration

The hardhat.config.ts file contains some ZKsync Era specific configurations:

The ZKsync Era deployment and compiler plugin imports:

Solidity project

import "@matterlabs/hardhat-zksync";

The zksolc block contains the minimal configuration for the compiler.

zksolc: {
  version: "latest", // Uses latest available in https://github.com/matter-labs/zksolc-bin
  settings: {},
},

Vyper project

import "@nomiclabs/hardhat-vyper";
import "@matterlabs/hardhat-zksync-deploy";
import "@matterlabs/hardhat-zksync-vyper";

The zkvyper block contains the minimal configuration for the compiler.

zkvyper: {
  version: "latest", // Uses latest available in https://github.com/matter-labs/zkvyper-bin
  settings: {},
},

Network

The network endpoints of the zkSyncTestnet network change dynamically for local tests.

// dynamically changes endpoints for local tests
const zkSyncTestnet =
  process.env.NODE_ENV == "test"
    ? {
        url: "http://localhost:3050",
        ethNetwork: "http://localhost:8545",
        zksync: true,
      }
    : {
        url: "https://sepolia.era.zksync.dev",
        ethNetwork: "sepolia",
        zksync: true,
      };

Set your Private Key

Rename .env.example to .env and set your private key:

WALLET_PRIVATE_KEY=YourPrivateKeyHere

Your private key will be used for paying the costs of deploying the smart contract.

Compile and deploy a contract

Smart contracts belong in the contracts folder.

1. To compile the contract, run

yarn hardhat compile

You'll see the following output:

Compiling 1 Solidity file
Successfully compiled 1 Solidity file
// Successfully compiled 1 Vyper file - Vyper project
✨  Done in 1.09s.

The artifacts-zk and cache-zk folders appear in the root directory (instead of the regular Hardhat's artifacts and cache). These folders contain the compilation artifacts (including contract's ABIs) and compiler cache files.

The deploy-greeter.ts script is in the deploy folder. This script uses the Deployer class from the hardhat-zksync-deploy package to deploy the Greeter.sol/Greeter.vy contract.

import { Wallet, utils } from "zksync-ethers";
import * as ethers from "ethers";
import { HardhatRuntimeEnvironment } from "hardhat/types";
import { Deployer } from "@matterlabs/hardhat-zksync-deploy";

// load env file
import dotenv from "dotenv";
dotenv.config();

// load wallet private key from env file
const PRIVATE_KEY = process.env.WALLET_PRIVATE_KEY || "";

if (!PRIVATE_KEY) throw "⛔️ Private key not detected! Add it to the .env file!";

// An example of a deploy script that will deploy and call a simple contract.
export default async function (hre: HardhatRuntimeEnvironment) {
  console.log(`Running deploy script for the Greeter contract`);

  // Initialize the wallet.
  const wallet = new Wallet(PRIVATE_KEY);

  // Create deployer object and load the artifact of the contract you want to deploy.
  const deployer = new Deployer(hre, wallet);
  const artifact = await deployer.loadArtifact("Greeter");

  // Estimate contract deployment fee
  const greeting = "Hi there!";
  const deploymentFee = await deployer.estimateDeployFee(artifact, [greeting]);

  // ⚠️ OPTIONAL: You can skip this block if your account already has funds in L2
  // const depositHandle = await deployer.zkWallet.deposit({
  //   to: deployer.zkWallet.address,
  //   token: utils.ETH_ADDRESS,
  //   amount: deploymentFee.mul(2),
  // });
  // // Wait until the deposit is processed on ZKsync
  // await depositHandle.wait();

  // Deploy this contract. The returned object will be of a `Contract` type, similar to ones in `ethers`.
  // `greeting` is an argument for contract constructor.
  const parsedFee = ethers.formatEther(deploymentFee);
  console.log(`The deployment is estimated to cost ${parsedFee} ETH`);

  const greeterContract = await deployer.deploy(artifact, [greeting]);

  // obtain the Constructor Arguments
  console.log("constructor args:" + greeterContract.interface.encodeDeploy([greeting]));

  // Show the contract info.
  const contractAddress = await greeterContract.getAddress();
  console.log(`${artifact.contractName} was deployed to ${contractAddress}`);
}

2. To execute the deployment script run

yarn hardhat deploy-zksync --script deploy-greeter.ts

This script deploys the Greeting contract with the message "Hi there!" to ZKsync Sepolia Testnet.

You should see something like this:

Running deploy script for the Greeter contract
The deployment is estimated to cost 0.00579276320831943 ETH
constructor args:0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000094869207468657265210000000000000000000000000000000000000000000000
Greeter was deployed to 0x46f1d2d8A16DBD8b47e9D61175a826ac667288Be4D1293a22E8

✨  Done in 12.69s.

Congratulations! You have deployed a smart contract project to ZKsync Sepolia Testnet with Hardhat 🎉

Interact with the contract

The template project contains another script to interact with the contract.

1. Enter the address of the deployed Greeter contract in the CONTRACT_ADDRESS variable of the use-greeter.ts script:
   use-greeter.ts

   import { Provider } from "zksync-ethers";
   import * as ethers from "ethers";
   import { HardhatRuntimeEnvironment } from "hardhat/types";
   
   // load env file
   import dotenv from "dotenv";
   dotenv.config();
   
   // load contract artifact. Make sure to compile first! - Solidity Project
   import * as ContractArtifact from "../artifacts-zk/contracts/Greeter.sol/Greeter.json";
   // load contract artifact. Make sure to compile first! - Vyper Project
   //import * as ContractArtifact from "../artifacts-zk/contracts/Greeter.vy/Greeter.json";
   
   const PRIVATE_KEY = process.env.WALLET_PRIVATE_KEY || "";
   
   if (!PRIVATE_KEY) throw "⛔️ Private key not detected! Add it to the .env file!";
   
   // Address of the contract on ZKsync testnet
   const CONTRACT_ADDRESS = "";
   
   if (!CONTRACT_ADDRESS) throw "⛔️ Contract address not provided";
   
   // An example of a deploy script that will deploy and call a simple contract.
   export default async function (hre: HardhatRuntimeEnvironment) {
     console.log(`Running script to interact with contract ${CONTRACT_ADDRESS}`);
   
     // Initialize the provider.
     // @ts-ignore
     const provider = new Provider(hre.userConfig.networks?.zkSyncTestnet?.url);
     const signer = new ethers.Wallet(PRIVATE_KEY, provider);
   
     // Initialise contract instance
     const contract = new ethers.Contract(CONTRACT_ADDRESS, ContractArtifact.abi, signer);
   
     // Read message from contract
     console.log(`The message is ${await contract.greet()}`);
   
     // send transaction to update the message
     const newMessage = "Hello people!";
     const tx = await contract.setGreeting(newMessage);
   
     console.log(`Transaction to change the message is ${tx.hash}`);
     await tx.wait();
   
     // Read message after transaction
     console.log(`The message now is ${await contract.greet()}`);
   }
   

2. To execute the script, run:

   yarn hardhat deploy-zksync --script use-greeter.ts
   

   
   The script will:
   • Retrieve the message from the contract by calling the greet() method.
   • Update the greeting message in the contract with the setGreeting() method.
   • Retrieve the message from the contract again.
   
   You should see something like this:

   Running script to interact with contract Greeter
   The message is Hello there!
   Transaction to change the message is 0x12f16578A16DB0f47e9D61175a823ac214288Af
   The message now is Hello people!
   
   ✨  Done in 14.32s.
   

Learn more

• To learn more about the ZKsync Hardhat plugins check out the plugins documentation.
• If you want to know more about how to interact with ZKsync using Javascript, check out the zksync-ethers Javascript SDK documentation.