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Getting started

Getting started

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

zkSync Era has the following official plugins for Hardhat:

Additional plugins

Learn more about other plugins from the community that you can use with zkSync Era.

To learn more about Hardhat itself, check out its official documentationopen in new window.

This tutorial shows you how to set up a zkSync Era Solidity project with Hardhat using the zkSync CLI.

If you are using Vyper, check out the Vyper plugin documentation or this exampleopen in new window in GitHub!

Prerequisites

Local zkSync Testing with zksync-cli

Skip the hassle for test ETH by using zksync-cli for local testing. Simply execute npx zksync-cli dev start to initialize a local zkSync development environment, which includes local Ethereum and zkSync nodes. This method allows you to test contracts without requesting external testnet funds. Explore more in the zksync-cli documentation.

Important

  • Contracts must be compiled using the official zkSync Era compilers, with their respective Hardhat plugins.
  • Contracts compiled with other compilers will fail to deploy to zkSync Era.

Project setup

To create a new project run the CLI's create command, passing a project name:

npx zksync-cli create-project demo --template hardhat_solidity

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.

Migrating a project

If you want to migrate an existing project, please check the project migration guide.

Hardhat configuration

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

The zkSync Era deployment and compiler plugin imports.

import "@matterlabs/hardhat-zksync-deploy";
import "@matterlabs/hardhat-zksync-solc";

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://testnet.era.zksync.dev",
        ethNetwork: "goerli",
        zksync: true,
      };

Info

For local zkSync testing, modify url and ethNetwork in hardhat.config.ts to align with your local zkSync and Ethereum node's L2 and L1 RPC URLs, respectively.

Unit tests

This template project includes a basic unit test in the /test folder that runs with the local-setup and can be executed with yarn test. Learn more about how to start the local setup and write unit tests here.

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: {},
},

Advanced configuration

To learn more about each specific property in the hardhat.config.ts file, check out the plugins documentation

Set your Private Key

Rename .env.example to .env and input 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. The template project contains a simple Greeter.sol contract and a script to deploy it.

  1. To compile the contract, run:
yarn hardhat compile

You'll see the following output:

Compiling 1 Solidity file
Successfully compiled 1 Solidity file
✨  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.

Tips

The artifacts-zk and cache-zk folders are included in the .gitignore file.

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 contract.

import { Wallet, utils } from "zksync-web3";
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, similarly to ones in `ethers`.
  // `greeting` is an argument for contract constructor.
  const parsedFee = ethers.utils.formatEther(deploymentFee.toString());
  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 = greeterContract.address;
  console.log(`${artifact.contractName} was deployed to ${contractAddress}`);
}
  1. 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 Era 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 Era Testnet with Hardhat 🎉

Request-Rate Exceeded message

  • This message is caused by using the default RPC endpoints provided by ethers.
  • To avoid this, use your own Goerli RPC endpoint in the hardhat.config.ts file.
  • Find multiple node providers hereopen in new window.

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:
import { Provider } from "zksync-web3";
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!
import * as ContractArtifact from "../artifacts-zk/contracts/Greeter.sol/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()}`);
}
  1. 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.

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