How to set private key for Ethers Signer

Question

I would like to invoke a smart contract function using Ethers library. Since I have my own node I'm connecting using RPC connection and now I would like to invoke a transfer function (of an ERC20 contract), which according to the documentation requires me to use a signer:

const provider = new ethers.providers.JsonRpcProvider(NODE_URL)
const signer = provider.getSigner()

// 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(erc20ContractAddress, abi, signer)
const tx = await erc20_rw.transfer(targetAddress, amount)

My question is: Where should I provide my private key? I mean - the provider requires me to give only a node url and the signer is provided by the provider. I'm invoking a transfer, which defiantly should require me to provide a private key at some point. What am I missing?

Answer 1

You could simply replace the 2nd line in your code above and instead define the signer as follows:

const signer = new ethers.Wallet(your_private_key_string, provider);

You could also define a signer from a mnemonic instead of a private key, as follows:

const account = utils.HDNode.fromMnemonic(your_mnemonic_string).derivePath(`m/44'/60'/0'/0/${your_selected_account}`);

const signer = new Wallet(account, provider);

Where your_selected_account is the account index to use, starting from 0.

Note: make sure to use the right derivation path for you (Ledger, MEW, Metamask, ..etc).

Answer 2

const pKey = new ethers.Wallet.createRandom();
const signer = new ethers.Wallet(pKey, provider);

Answer 3

const provider = new ethers.providers.JsonRpcProvider(URL);
const wallet = new ethers.Wallet(WALLET_SECRET_KEY);
// connect the wallet to the provider
const signer = wallet.connect(provider);