Example of creating a BaseTx using Avalanche.js with multiple Secp256k1 inputs and outputs of different assetIDs for the Avalanche network

multi-secp-tx.ts

// The setup
// AVAX Balance
// curl -X POST --data '{
//     "jsonrpc":"2.0",
//     "id"     : 1,
//     "method" :"avm.getBalance",
//     "params" :{
//         "address":"X-EKpEPX56YA1dsaHBsW8X5nGqNSwJ7JrWH",
//         "assetID": "AVA"
//     }
//   }' -H 'content-type:application/json;' 127.0.0.1:9650/ext/bc/X
// {"jsonrpc":"2.0","result":{"balance":"20000","utxoIDs":[{"txID":"2QYFsMGEgNPsy4gy2wFnNMYmVkLQg9wMLmns5kTH3YJv6FiXLi","outputIndex":0}]},"id":1}
//
// 2pYGetDWyKdHxpFxh2LHeoLNCH6H5vxxCxHQtFnnFaYxLsqtHC Balance
// X-Address: X-EKpEPX56YA1dsaHBsW8X5nGqNSwJ7JrWH
// assetID: 2pYGetDWyKdHxpFxh2LHeoLNCH6H5vxxCxHQtFnnFaYxLsqtHC
// curl -X POST --data '{
//     "jsonrpc":"2.0",
//     "id"     : 1,
//     "method" :"avm.getBalance",
//     "params" :{
//         "address":"X-EKpEPX56YA1dsaHBsW8X5nGqNSwJ7JrWH",
//         "assetID": "2pYGetDWyKdHxpFxh2LHeoLNCH6H5vxxCxHQtFnnFaYxLsqtHC"
//     }
//   }' -H 'content-type:application/json;' 127.0.0.1:9650/ext/bc/X
//   {"jsonrpc":"2.0","result":{"balance":"299999999999900","utxoIDs":[{"txID":"dGFvs8JyGLhAUV4N5BY6VotbrqvjqnXfDPk1gdPBVY8HBvnrB","outputIndex":0}]},"id":1}
// 

// imports
import {Avalanche, BinTools, AVM, AVMKeyChain, TransferableInput, TransferableOutput, BaseTx, UnsignedTx, SecpInput, SecpOutput, Tx} from "avalanche" 
import BN from 'bn.js';
import { Buffer } from 'buffer/'; 

const ip: string = "ip.address.of.node"
const port: number = 9650
const protocol: string = "http"
const networkId: number = 3
const avalanche: Avalanche = new Avalanche(ip, port, protocol, networkId)
const avm: AVM = avalanche.AVM()
const bintools: BinTools = BinTools.getInstance()
const myKeychain: AVMKeyChain = avm.keyChain()

// the goods
const main = async (): Promise<any> => {
  const mypk: Buffer = bintools.avaDeserialize("privkey")
  myKeychain.importKey(mypk)
  const txid1: Buffer = bintools.avaDeserialize("2QYFsMGEgNPsy4gy2wFnNMYmVkLQg9wMLmns5kTH3YJv6FiXLi")
  const txid2: Buffer = bintools.avaDeserialize("dGFvs8JyGLhAUV4N5BY6VotbrqvjqnXfDPk1gdPBVY8HBvnrB")
  // assetid1 is the AVAX assetID
  const assetid1: Buffer = bintools.avaDeserialize("21d7KVtPrubc5fHr6CGNcgbUb4seUjmZKr35ZX7BZb5iP8pXWA")
  const assetid2: Buffer = bintools.avaDeserialize("2pYGetDWyKdHxpFxh2LHeoLNCH6H5vxxCxHQtFnnFaYxLsqtHC")
  // blockchainID is the Denali default subnet's X-Chain ID
  const blockchainID: Buffer = bintools.avaDeserialize("rrEWX7gc7D9mwcdrdBxBTdqh1a7WDVsMuadhTZgyXfFcRz45L")
  const addresses: Buffer[] = myKeychain.getAddresses()
  const ins: TransferableInput[] = []
  const outs: TransferableOutput[] = []
  const amt1: BN = new BN(20000)
  const amt2: BN = new BN(299999999999900)
  const output1: SecpOutput = new SecpOutput(amt1, new BN(1), 1, addresses)
  const output2: SecpOutput = new SecpOutput(amt2, new BN(1), 1, addresses)

  const transferableOutput1: TransferableOutput = new TransferableOutput(assetid1, output1)
  const transferableOutput2: TransferableOutput = new TransferableOutput(assetid2, output2)
  outs.push(transferableOutput1)
  outs.push(transferableOutput2)

  const input1: SecpInput = new SecpInput(amt1)
  const input2: SecpInput = new SecpInput(amt2)
  input1.addSignatureIdx(0, addresses[0])
  input2.addSignatureIdx(0, addresses[0])

  const outputIndex1: Buffer = Buffer.from(bintools.fromBNToBuffer(new BN(0), 4))
  const transferableInput1: TransferableInput = new TransferableInput(txid1, outputIndex1, assetid1, input1)
  const outputIndex2: Buffer = Buffer.from(bintools.fromBNToBuffer(new BN(0), 4))
  const transferableInput2: TransferableInput = new TransferableInput(txid2, outputIndex2, assetid2, input2)
  ins.push(transferableInput1)
  ins.push(transferableInput2)

  const baseTx: BaseTx = new BaseTx(networkId, blockchainID, outs, ins)
  const unsignedTx: UnsignedTx = new UnsignedTx(baseTx)
  const tx: Tx = unsignedTx.sign(myKeychain) 
  const transactionId: string = await avm.issueTx(tx)
  console.log(transactionId)
  // 224FTv4PTTgvdc5T1tioZ45u4NbKXmEqbjdnBkPrGzX3C9LkRE
}

main()