Blockchain Development Programming Tutorials, Guides & Best Practices

• ethers.randomBytes:
• Library: ethers.randomBytes is provided by the ethers.js library, a popular JavaScript library for Ethereum development. You need to install and include ethers.js as a dependency in your project to use this function.
• Usage: This function optionally takes the number of bytes you want to generate. If no argument is passed, it defaults to generating 32 bytes. It returns a Uint8Array of random bytes.
• Example:

    const { ethers } = require('ethers');
    const randomBytes = ethers.utils.randomBytes(32);
    console.log(randomBytes); // Uint8Array of random bytes

By the end of this tutorial, you will be able to:

• Query the balance of ERC-20 tokens for an Ethereum address.
• Retrieve ERC-20 token transfer histories using the Etherscan API.

• Rate Limits: Etherscan’s free tier limits the number of API requests per second (usually around 5 per second). This is fine for querying data but can be limiting for large-scale applications that need to process a lot of data quickly.
• Pricing: Etherscan offers paid tiers that increase the API request limits.

• Rate Limits: Infura’s free tier provides a generous number of requests (e.g., 100,000 requests per day) and supports more requests as you scale. This makes it more suitable for real-time dApps.
• Pricing: Infura’s paid plans offer higher limits and additional features like access to Layer 2 networks.

Deploying smart contracts is a more advanced topic, but here’s an example of how you can use Ethers.js with Infura to deploy a smart contract:

const ethers = require('ethers');

// Replace with your Infura Project ID
const infuraProvider = new ethers.JsonRpcProvider('https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID');

// Replace with your private key
const privateKey = 'YOUR_PRIVATE_KEY';

// Create a wallet instance and connect it to Infura
const wallet = new ethers.Wallet(privateKey, infuraProvider);

// Contract bytecode and ABI
const bytecode = '0xYourContractBytecode';
const abi = [
    // Your contract ABI here
];

async function deployContract() {
    try {
        // Create a ContractFactory to deploy the contract
        const factory = new ethers.ContractFactory(abi, bytecode, wallet);

        // Deploy the contract
        const contract = await factory.deploy();

        // Wait for the contract to be mined
        console.log('Contract deployed at address:', contract.address);
        await contract.deployTransaction.wait();
    } catch (error) {
        console.error('Error deploying contract:', error);
    }
}

// Call the function to deploy the contract
deployContract();

const axios = require('axios');

// Replace this with your actual Etherscan API key
const apiKey = 'YOUR_ETHERSCAN_API_KEY';

// Replace this with the Ethereum address you want to query
const address = '0xYourEthereumAddress';

// Replace this with the contract address of the ERC-20 token
const contractAddress = '0xYourTokenContractAddress';

// Etherscan API URL to fetch the ERC-20 token balance
const url = `https://api.etherscan.io/api?module=account&action=tokenbalance&contractaddress=${contractAddress}&address=${address}&tag=latest&apikey=${apiKey}`;

async function getTokenBalance() {
  try {
    // Make the API request to Etherscan
    const response = await axios.get(url);
    const tokenBalance = response.data.result;

    // Log the token balance (Note: Token balances are often in very small denominations)
    console.log(`Token Balance: ${tokenBalance}`);
  } catch (error) {
    console.error('Error fetching token balance:', error);
  }
}

// Call the function to get the token balance
getTokenBalance();

• Replace 'YOUR_ETHERSCAN_API_KEY' with your Etherscan API key.
• Replace '0xYourEthereumAddress' with the address you want to query.
• Replace '0xYourTokenContractAddress' with the ERC-20 token's contract address (e.g., USDT or DAI token contract).
• This script queries the ERC-20 token balance for a specific Ethereum address.