Web3 & Ethereum Basics Cheat Sheet

// SPDX-License-Identifier: MITpragma solidity ^0.8.20;contract SimpleStorage {    uint256 private value;    address public owner;    event ValueChanged(uint256 newValue);    constructor() {        owner = msg.sender; // deployer becomes the owner    }    function setValue(uint256 _value) public {        require(msg.sender == owner, "Not authorized");        value = _value;        emit ValueChanged(_value);    }    function getValue() public view returns (uint256) {        return value; // 'view' = no gas cost when called off-chain    }}

import { ethers } from 'ethers';// Read-only provider (no signing capability)const provider = new ethers.JsonRpcProvider('https://sepolia.infura.io/v3/YOUR_KEY');// Signer wraps a private key/wallet for sending transactionsconst wallet = new ethers.Wallet(process.env.PRIVATE_KEY, provider);const abi = ['function getValue() view returns (uint256)', 'function setValue(uint256)'];const contract = new ethers.Contract('0xContractAddress...', abi, wallet);// Read call — free, no transaction, no gasconst current = await contract.getValue();// Write call — creates a signed transaction, costs gas, needs confirmationconst tx = await contract.setValue(42);const receipt = await tx.wait(); // waits for the tx to be minedconsole.log('Confirmed in block', receipt.blockNumber);