BitcoinJS: JavaScript Bitcoin library for applications

const bitcoin = require('bitcoinjs-lib');
const ECPair = require('ecpair');

// Create a key pair
const keyPair = ECPair.makeRandom();
const { address } = bitcoin.payments.p2pkh({ pubkey: keyPair.publicKey });

// Create a new transaction builder
const psbt = new bitcoin.Psbt({ network: bitcoin.networks.testnet });

// Add an input (previous transaction output)
psbt.addInput({
  hash: 'e9b542c176808992facac58c46e36ccd2b2e0c7ae0b5c2e4e6b8f0a6e8b5c2d1',
  index: 0,
  witnessUtxo: {
    script: bitcoin.address.toOutputScript(address, bitcoin.networks.testnet),
    value: 100000 // satoshis
  }
});

// Add an output
psbt.addOutput({
  address: 'tb1qw508d6qejxtdg4y5r3zarvary0c5xw7kxpjzsx',
  value: 90000 // leaving 10000 satoshis for fee
});

// Sign the transaction
psbt.signInput(0, keyPair);
psbt.validateSignaturesOfInput(0);
psbt.finalizeAllInputs();

// Extract the transaction
const tx = psbt.extractTransaction();
console.log('Transaction hex:', tx.toHex());
console.log('Transaction ID:', tx.getId());