ecdsaSign.js

const { ethers } = require("ethers");

async function sign(privKey, message) {

    // Create a Wallet instance
    const wallet = new ethers.Wallet(privKey);
  
    // Sign the message
    const signature = await wallet.signMessage(message);

    // Parse the signature and get r and s
    // r is "0x" + sig.slice(2, 2 + 64))
    // s is "0x" + sig.slice(66, 66 + 64)
    const rHex = "0x" + signature.slice(2, 2 + 64);
    const sHex = "0x" + signature.slice(66, 66 + 64);

    const r = ethers.utils.arrayify(rHex).reverse();
    const s = ethers.utils.arrayify(sHex).reverse();

    // Compute the hash of the message
    const messageHashHex = ethers.utils.hashMessage(message);

    // Convert message hash from hex to byte array
    const messageHash = ethers.utils.arrayify(messageHashHex).reverse();
    
    // add 0x to the private key and convert to byte array
    const privKeyHex = "0x" + privKey;
    const privKeyBytes = ethers.utils.arrayify(privKeyHex).reverse();

    return {
        privKeyHex,
        privKeyBytes,
        signature,
        rHex,
        r,
        sHex,
        s,
        messageHashHex,
        messageHash,
    };

}

signAndCompute('[YOUR PRIVATE KEY]', 'helloworld!')
    .then(console.log)
    .catch(console.error);