L2 counter contract

L2 Counter

Now that we have an address for the L1 governance contract, we can build, deploy, and test the counter contract on L2.

1. cd out of L1-governance and initialize the L2-counter project:

   npx zksync-cli create L2-counter --template hardhat_solidity
   

2. For the purposes of this tutorial, we don't need the example smart contracts and deployment script files generated by zksync-cli. Run the following commands to remove them:

   cd L2-counter
   rm -rf ./contracts/*
   rm -rf ./scripts/*
   

Create L2 Counter Contract

1. In the L2-counter/contracts/ directory, create a new file Counter.sol.

   touch contracts/Counter.sol
   

   
   This contract contains the address of the governance contract deployed previously on layer 1, and an incrementable counter which can only be invoked by the governance contract.
2. Copy/paste the following code into the file:
   Counter.sol

   // SPDX-License-Identifier: Unlicense
   
   pragma solidity ^0.8.17;
   
   contract Counter {
     uint256 public value = 0;
     address public governance;
   
     constructor(address newGovernance) {
       governance = newGovernance;
     }
   
     function increment() public {
       require(msg.sender == governance, 'Only governance is allowed');
   
       value += 1;
     }
   }
   

3. Compile the contract from the L2-counter root:
   Compilations happens only after the installation of a compiler.
   npmyarnpnpmbun

   npm run compile
   

Deploy L2 Counter Contract

1. Create a new file inside the scripts folder named deploy.ts.

   touch scripts/deploy.ts
   

2. Copy/paste the following code into L2-counter/scripts/deploy.ts, replacing <GOVERNANCE-ADDRESS> with the address of the Governance contract we just deployed:
   L2-counter/scripts/deploy.ts

   import { ethers, network } from 'hardhat';
   import { utils } from 'zksync-ethers';
   
   const GOVERNANCE_ADDRESS = process.env.GOVERNANCE_ADDRESS ?? '<GOVERNANCE-ADDRESS>';
   
   async function main() {
     const CONTRACT_NAME = 'Counter';
     const ARGS = [utils.applyL1ToL2Alias(GOVERNANCE_ADDRESS)];
     console.log(`Deploying ${CONTRACT_NAME} contract to ${network.name}`);
     const contract = await ethers.deployContract(CONTRACT_NAME, ARGS, {});
     await contract.waitForDeployment();
     const contractAddress = await contract.getAddress();
     console.log(`${CONTRACT_NAME} deployed to ${contractAddress}`);
   }
   
   main()
     .then(() => process.exit(0))
     .catch((error) => {
       console.error(error);
       process.exit(1);
     });
   

3. Now deploy the contract from the L2-counter/ folder root to ZKsync Era Sepolia:
   npmyarnpnpmbun

   npm run deploy
   

   
   You should see output like this:

   Deploying Counter contract to ZKsyncEraSepolia
   Counter deployed to 0x111C3E89Ce80e62EE88318C2804920D4c96f92bb
   

Read the Counter Value

Now both contracts are deployed, we can create a script to retrieve the value of the counter.

1. Create a new file in the scripts folder named display-value.ts.

   touch scripts/display-value.ts
   

2. Copy and paste in the following code, adding the deployed counter contract address:
   L2-counter/scripts/display-value.ts

   import { ethers } from 'hardhat';
   
   async function main() {
     const COUNTER_ADDRESS = process.env.COUNTER_ADDRESS ?? '<COUNTER_ADDRESS>';
   
     const [signer] = await ethers.getSigners();
     const counterFactory = await ethers.getContractFactory('Counter');
     const counterContract = counterFactory.connect(signer).attach(COUNTER_ADDRESS);
   
     const value = (await counterContract.value()).toString();
     console.log(`The counter value is ${value}`);
   }
   
   main()
     .then(() => process.exit(0))
     .catch((error) => {
       console.error(error);
       process.exit(1);
     });
   

3. Run the script:
   npmyarnpnpmbun

   npx hardhat run ./scripts/display-value.ts
   

   
   The output should be:

   The counter value is 0