const envelopeType = StellarSdk.xdr.EnvelopeType.envelopeTypeTx().toXDR();
const signatureBase = Buffer.concat([networkId, envelopeType, txXDR])
const transactionHash = StellarSdk.hash(signatureBase);
networkId = ?
envelopeType = ?
txXDR = ?
What are these variables equal to, example ordinary transaction.