priv2pub.js

const {randomBytes} = require("crypto")
const secp256k1 = require("secp256k1")

// or require('secp256k1/elliptic')
//   if you want to use pure js implementation in node

// generate message to sign
// message should have 32-byte length, if you have some other length you can hash message
// for example `msg = sha256(rawMessage)`
const msg = randomBytes(32)

// generate privKey
let privKey
do {
  privKey = randomBytes(32)
} while (!secp256k1.privateKeyVerify(privKey))

// get the public key in a compressed format
const pubKey = secp256k1.publicKeyCreate(privKey)

function toHex(buffer) {
  return Array.from(buffer)
    .map(byte => byte.toString(16).padStart(2, "0"))
    .join("")
}

console.log("pub key", toHex(pubKey), pubKey.toString("hex"))
// sign the message
const sigObj = secp256k1.ecdsaSign(msg, privKey)

// verify the signature
console.log(secp256k1.ecdsaVerify(sigObj.signature, msg, pubKey))
// => true