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

Community: Website wtf.academy | WTF Solidity | discord | WeChat Group Application

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

In this lesson, we will introduce the Provider class in ethers.js and use it to connect to a node to retrieve information from the blockchain.

Provider Class

The Provider class provides an abstraction for connecting to the Ethereum network and offers a concise and consistent interface for standard Ethereum node functionality. In ethers, the Provider class does not handle user private keys and can only read information from the blockchain, making it safer compared to web3.js.

The most commonly used provider in ethers is jsonRpcProvider, which allows users to connect to a specific node service provider.

jsonRpcProvider

Creating an API Key for the Node Service Provider

First, you need to register and create an API Key on the website of the node service provider (e.g INFURA, ALCHEMY). In the "Tools" section of the "WTF Solidity" tutorial, we introduced the methods to create API Keys for two projects, Infura and Alchemy. You can refer to the tutorial for more information.

Connecting to Infura Node

Here, we will use Infura as an example. After creating the Infura API Key, you can create a Provider variable using the ethers.JsonRpcProvider() method, which takes the URL of the node service as a parameter.

In the following example, we create providers to connect to the ETH mainnet and the Sepolia testnet:

// Connect to the Ethereum network using Infura's RPC node
const INFURA_MAINNET_URL = 'https://mainnet.infura.io/v3/8b9750710d56460d940aeff479672b3a';
const INFURA_SEPOLIA_URL = 'https://sepolia.infura.io/v3/8b9750710d56460d940aeff479672b3a';
// Connect to the Ethereum mainnet
const providerETH = new ethers.JsonRpcProvider(INFURA_MAINNET_URL)
// Connect to the Sepolia testing network
const providerSepolia = new ethers.JsonRpcProvider(INFURA_SEPOLIA_URL)

Using the Provider to Retrieve Blockchain Data

The Provider class provides convenient methods to retrieve data from the blockchain:

1. Use the getBalance() function to retrieve the ETH balance of Vitalik on the mainnet and the Sepolia testnet:

// 1. Retrieve the ETH balance of Vitalik on the mainnet and the Sepolia testnet
    console.log("1. Retrieving the ETH balance of Vitalik on the mainnet and the Sepolia testnet");
    const balanceETH = await providerETH.getBalance(`vitalik.eth`);
    const balanceSepolia = await providerSepolia.getBalance(`vitalik.eth`);
    // Output the balances on the console (mainnet)
    console.log(`\nETH Balance of ${address} --> ${ethers.formatEther(balanceETH)} ETH\n`)
    // Output the Sepolia testnet ETH balance
    console.log(`\nSepoliaETH Balance of ${address} --> ${ethers.formatEther(balanceSepolia)} ETH\n`)

2. Use the getNetwork() function to check which chain the provider is connected to.

// 2. Check which chain the provider is connected to
      const network1 = await provider1.getNetwork();
      const network2 = await provider2.getNetwork();

  console.log("Network 1:", network1.name, "ID:", network1.chainId);
  console.log("Network 2:", network2.name, "ID:", network2.chainId);

3. Use the getBlockNumber() function to retrieve the current block number:

// 3. Retrieve the current block number
const main = async () => {
  const blockNumber = await provider1.getBlockNumber();
  console.log(blockNumber);
};

4. Use the getTransactionCount() function to retrieve the transaction count of a wallet address.

// 4. Retrieve the transaction count of Vitalik's wallet
const main = async () => {
  const txcount = await provider1.getTransactionCount('vitalik.eth');
  console.log(txcount);
};

5. Use the getFeeData() function to retrieve the current recommended gas settings, which are returned as bigint.

// 5. Retrieve the current recommended gas settings
const main = async () => {
  const feeData = await provider1.getFeeData();
  console.log(feeData);
};

6. Use the getBlock() function to retrieve information about a specific block. The parameter is the block number:

// 6. Retrieve information about a specific block
const main = async () => {
  const block = await provider1.getBlock(0);
  console.log(block);
};

7. Use the getCode() function to retrieve the bytecode of a contract at a specific address. In the example below, we use the contract address of WETH on the mainnet:

// 7. Retrieve the bytecode of a contract at a specific address, using the contract address of WETH on the mainnet as an example
const main = async () => {
  const bytecode = await provider1.getCode('0xc778417e063141139fce010982780140aa0cd5ab');
  console.log(bytecode);
};

Summary

In this lesson, we introduced the Provider class of ethers.js and created a jsonRpcProvider with Infura's node API key to read on-chain information from the ETH main network and Sepolia test network.