Hardhat Smart Contract Lottery - Free Code Camp Tutorial

Setting up:

• We used this very long command to install all of our dependencies for this project:

yarn add --dev @nomiclabs/hardhat-ethers@npm:hardhat-deploy-ethers ethers @nomiclabs/hardhat-etherscan @nomiclabs/hardhat-waffle chai ethereum-waffle hardhat hardhat-contract-sizer hardhat-deploy hardhat-gas-reporter prettier prettier-plugin-solidity solhint solidity-coverage dotenv

Note: then, need to add require statements to hardhat.config.js

Events:

• Whenever we update a dynamic object (like an array, mapping), always emit an event
• EVM has functionality to log events - events allow you to "print" to the EVM log
• Smart contracts cannot access logs, but emitted events are tied to the contract that emitted them
• Within events, parameters are either indexed or not; can have up to 3 indexed parameters (topics); these are much easier to search for
• Naming convention: name an event (function_start) by the reverse of a function (start_function)

Chainlink VRF and keepers:

• Biggest change in VRF version 2 is that instead of funding contract with link (VRF 1 model), instead now funding subscription, an account that allows you to fund multiple contracts
• Happens in two parts: request the random words, then fulfill random words - this being a two-part process helps prevent hacking/breaking the randomness of the process
• The vrfCoordinator is the address of the contract that does the random number verification
• How to use keepers network to automate parts of our code, based on a trigger we define:

need to make sure our contract has two functions: checkUpkeep (checks if the contract requires work to be done) and performUpkeep (perform the work on the contract, if instructed by checkUpkeep)

checkUpkeep is run off-chain by a node from the chainlink keeper network performUpkeep: where we verify that things are correct and should run on chain

Other notes:

• If we want an address to be able to receive tokens (whether we're receiving or sending), the address needs to have the payable keyword
• hardhat-shorthand is an NPM package that will allow us to be able to type "hh compile" rather than "yarn hardhat compile", and similar commands; to install, yarn global add hardhat-shorthand (correction: that installation command does not work; use npm install --global hardhat-shorthand)
• Transactions which are performed through the VRF coordinator will not show up on the main transactions page (in the block explorer), but rather under internal transactions

Resolving errors:

• If you get something that looks like this "TypeError: Cannot read properties of undefined (reading 'emit')" when trying to run tests using expect, probably need to move parentheses around

the syntax is expect(some_function()).to...

• Error: VM Exception while processing transaction: reverted with custom error 'InvalidConsumer()'

update the chainlink version: npm i --save-dev @chainlink/contracts@0.4.0

• If when running the 99-update-front-end.js script, it says there's a problem with JSON.parse and "SyntaxError: Unexpected end of JSON input", make sure the json files I'm trying to write to (abi.json, etc) only have {} as their content, or {} with a newline inside