Ethers 101

I've been revisiting ethers.js recently to refresh my understanding of the details and to write a simple tutorial called "WTF Ethers" for beginners.

Twitter: @0xAA_Science

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All the code and tutorials are open-sourced on GitHub: github.com/WTFAcademy/WTF-Ethers

In this lesson, we will introduce the ContractFactory type in ethers.js and use it to deploy a contract.

Deploying Smart Contracts

On Ethereum, deploying a smart contract is a special transaction: it involves sending the bytecode (creation code) obtained from compiling the smart contract to null address. If the contract has constructor arguments, you need to encode the arguments into bytecode using abi.encode and append it to the end of the contract bytecode. For an introduction to ABI encoding, refer to the WTF Solidity Tutorial Lesson 27: ABI Encoding.

Contract Factory

ethers.js provides the ContractFactory type that allows developers to easily deploy contracts. You can create an instance of ContractFactory by providing the contract's ABI, compiled bytecode, and the signer variable to prepare for contract deployment.

const contractFactory = new ethers.ContractFactory(ABI, bytecode, signer);

Note: If the contract has a constructor with arguments, the ABI must include the constructor.

After creating an instance of the contract factory, you can call its deploy function and pass the arguments args of the contract constructor to deploy and obtain an instance of the contract:

const contract = await contractFactory.deploy(args);

You can wait for the contract to be deployed and confirmed on the chain before interacting with it using either of the following commands:

await contractERC20.waitForDeployment();

Example: Deploying an ERC20 Token Contract

For an introduction to the ERC20 standard token contract, refer to the WTF Solidity Quick Start Lesson 31: ERC20.

1. Create provider and wallet variables.

   const { ethers } = require("ethers");
   
   // Connect to the Ethereum network using Infura's RPC node
   // Connect to the Sepolia test network
   const INFURA_SEPOLIA_URL = 'https://sepolia.infura.io/v3/8b9750710d56460d940aeff47967c4ba';
   const provider = new ethers.JsonRpcProvider(INFURA_GOERLI_URL);
   
   // Create a wallet object using the private key and provider
   const privateKey = '0x227dbb8586117d55284e26620bc76534dfbd2394be34cf4a09cb775d593b6f2b';
   const wallet = new ethers.Wallet(privateKey, provider);

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2. Prepare the bytecode and ABI of the ERC20 contract. Since the ERC20 contract has a constructor with arguments, we must include it in the ABI. You can obtain the contract bytecode by clicking the Bytecode button in the compilation panel of Remix. The "object" field corresponds to the bytecode data. If the contract is already deployed onchain, you can find it in the Contract Creation Code section on etherscan.

// Human-readable ABI of ERC20
 const abiERC20 = [
     "constructor(string memory name_, string memory symbol_)",
     "function name() view returns (string)",
     "function symbol() view returns (string)",
     "function totalSupply() view returns (uint256)",
     "function balanceOf(address) view returns (uint)",
     "function transfer(address to, uint256 amount) external returns (bool)",
     "function mint(uint amount) external",
 ];
 // Fill in the contract bytecode. In Remix, you can find the bytecode in two places:
 // 1. Click the Bytecode button in the compilation panel.
 // 2. In the artifact file with the same name as the contract in the file panel's artifact folder.
 // The data corresponding to the "object" field under the "bytecode" attribute is the bytecode, which is quite long, starting with 608060
 // "object": "608060405260646000553480156100...
 const bytecodeERC20 = "608060405260646000553480156100...";

3. Create an instance of the contract factory ContractFactory.

   const factoryERC20 = new ethers.ContractFactory(abiERC20, bytecodeERC20, wallet);

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4. Call the deploy() function of the factory contract and provide the constructor arguments (token, name and symbol) to deploy the ERC20 token contract and obtain the contract instance. You can use:

   • contract.target to get the contract address,
   • contract.deployTransaction to get the deployment details,
   • contractERC20.waitForDeployment() to wait for confirmation of contract deployment on the blockchain.

   // 1. Deploy the ERC20 token contract using contractFactory
   console.log("\n1. Deploy the ERC20 token contract using contractFactory")
   // Deploy the contract and provide constructor arguments
   const contractERC20 = await factoryERC20.deploy("WTF Token", "WTF")
   console.log(`Contract Address: ${contractERC20.target}`);
   console.log("Deployment transaction details")
   console.log(contractERC20.deploymentTransaction())
   console.log("\nWait for contract deployment on the blockchain")
   await contractERC20.waitForDeployment()
   // You can also use contractERC20.deployTransaction.wait()
   console.log("Contract deployed on the blockchain")

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5. After the contract is deployed on the blockchain, call the name() and symbol() functions to print the token name and symbol. Then call the mint() function to mint 10,000 tokens for yourself.

   // Print the contract's name() and symbol(), then call the mint() function to mint 10,000 tokens for your address
   console.log("\n2. Call the mint() function to mint 10,000 tokens for your address")
   console.log(`Contract Name: ${await contractERC20.name()}`)
   console.log(`Contract Symbol: ${await contractERC20.symbol()}`)
   const tx = await contractERC20.mint("10000")
   console.log("Wait for the transaction to be confirmed on the blockchain")
   await tx.waitForDeployment()
   console.log(`Token balance in your address after minting: ${await contractERC20.balanceOf(wallet)}`)
   console.log(`Total token supply: ${await contractERC20.totalSupply()}`)

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6. Call the transfer() function to transfer 1100 tokens to Vitalik.

   // 3. Call the transfer() function to transfer 1000 tokens to Vitalik
   console.log("\n3. Call the transfer() function to transfer 1100 tokens to Vitalik")
   const tx2 = await contractERC20.transfer("vitalik.eth", "1100")
   console.log("Wait for the transaction to be confirmed on the blockchain")
   await tx2.wait()
   console.log(`Token balance in Vitalik's wallet: ${await contractERC20.balanceOf("vitalik.eth")}`)

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Summary

In this lesson, we introduced the ContractFactory type in ethers.js and used it to deploy an ERC20 token contract and transfer 1100 tokens to Vitalik. Notice the gas deduction.