// A Human-Readable ABI; any supported ABI format could be used
const abi = [
    // Read-Only Functions
    "function balanceOf(address owner) view returns (uint256)",
    "function decimals() view returns (uint8)",
    "function symbol() view returns (string)",

    // Authenticated Functions
    "function transfer(address to, uint amount) returns (boolean)",

    // Events
    "event Transfer(address indexed from, address indexed to, uint amount)"
];

// This can be an address or an ENS name
const address = "demotoken.ethers.eth";

// An example Provider (connceted to testnet)
const provider = ethers.getDefaultProvider("ropsten");

// An example Signer
const signer = ethers.Wallet.createRandom(provider);

// Read-Only; By connecting to a Provider, allows:
// - Any constant function
// - Querying Filters
// - Populating Unsigned Transactions for non-constant methods
// - Estimating Gas for non-constant (as an anonymous sender)
// - Static Calling non-constant methods (as anonymous sender)
const erc20 = new ethers.Contract(address, abi, provider);

// Read-Write; By connecting to a Signer, allows:
// - Everything from Read-Only (except as Signer, not anonymous)
// - Sending transactions for non-constant functions
const erc20_rw = new ethers.Contract(address, abi, signer)