import { Buffer } from 'node:buffer';
const privatekey = "1111111111111111111111111111111111111111" // remove 0x
const cryptoType = "00" // 00 ed25519 01 secp256k1 02 secp256r1
let str = Buffer.from(cryptoType+privatekey,'hex')
console.log(str.toString("base64"))
save the code as base.js
run node base.js