_section: Quick Start


_subsection: Connecting to Ethereum: Metamask

The quickest and easiest way to experiment and begin
developing on Ethereum is to use [[link-metamask]],
which is a browser extension that provider:

- A connection to the Ethereum network
- Holds your private key and can sign thing

_code: Connecting to Metamask

// A Web3Provider wraps a standard Web3 provider, which is
// what Metamask injects into every page you visit as window.ethereum
const provider = new ethers.providers.Web3Provider(window.ethereum)

// The Metamask plugin also allows signing transactions to send ether
// and pay to change state within the blockchain. For this, we need
// the account signer...
const signer = provider.getSigner()


_heading: Querying the Blockchain

Once you have a [[Provider]], you have a read-only connection to the
blockchain, which can be used to query the current state, fetch historic
logs, look up deployed code and so on.

_code: Basic Queries

// <hide>
const provider = ethers.getDefaultProvider();
// </hide>

// Look up the current block number
provider.getBlockNumber()

// Get the balance of an account (by address or ENS name)
provider.getBalance("ethers.eth")


_heading: Writing to the Blockchain

Every write costs ... etc

_code: Sending Ether

// Send 1 ether to an ens name.
const tx = signer.sendTransaction({
    to: "ricmoo.firefly.eth",
    value: ethers.utils.parseEther("1.0")
});


_subsection: Contracts

_heading: Connecting to a Contract

To connect to an contract...

Explain ABI

Explain meta-class and the aBI

_code: Connecting to a Contract

// The ERC-20 Contract ABI, which is a common contract interface
// for tokens.
const abi = [
    // Some simple details about the token
    "function namd() view returns (string)",
    "function symbol() view returns (string)",

    // Get the account balance
    "function balanceOf(address) view returns (uint)",

    // Send some of your tokens to someone else
    "function transfer(address to, uint amount")",

    // An event triggered whenever anyone transfers to someone else
    "event Transfer(address indexed from, address indexed to, uint amount)"
];

const contract = new ethers.Contract(address, abi, provider);

const contract = new ethers.Contract(address, abi, provider);


_heading: Read-Only Methods

_code: Querying the DAI Contract

// <hide>
// </hide>

const contract = new Contract("dai.tokens.ethers.eth", abi, provider);

contract.name()
//!

contract.symbol()
//!

contract.balanceOf("ricmoo.firefly.eth")
//!


_heading: State Changing Methods

_heading: Listening to Events

_code: Listening to Events

// <hide>
const contract = ...
// </hide>

// Receive an event when ANY transfer occurs
contract.on("Transfer", (from, to, amount, event) => {
    console.log(`${ from } sent ${ formatEther(amount) } to ${ to}`);
});

// Receive an event when a specific address receives a token
const filter = contract.filters.Transfer(null, address)
contract.on(filter, (from, to, amount, event) => {
    // The to will always be "address"
    console.log(`I got ${ formatEther(amount) } from ${ from }.`);
});


_heading: Listing Historic Events

_code: Historic Events by Name

// List all transfers from anyone to anyone in the first XXX
contract.queryFilter("Transfer", 0, XXX)
//!


_code: Filtering Historic Events

// <hide>
const contract = ...
// </hide>

const address = signer.getAddress()

// Filter for all token transfers we've sent
const filterFrom = contract.filter.Transfer(address, null);
// <hide>
filterFrom
// </hide>
//!

// Filter for all token transfers we've received
const filterTo = contract.filter.Transfer(null, address);
// <hide>
filterTo
// </hide>
//!

// List all transfers we've sent between ...
contract.queryFilter(filterFrom, 0, 100000)
//!

// List all transfers we've received in blockhash XXX
contract.queryFilter(filterTo, XXX)
//!


_subsection: Signing Messages