Technical Bitcoin

2. Inspect the runnable source

// Run with Node 22+ after saving as transaction.mjs.
import { createHash } from "node:crypto";

const project = {
  "version": 2,
  "locktime": 0,
  "inputs": [
    {
      "txid": "1111111111111111111111111111111111111111111111111111111111111111",
      "vout": 1,
      "sequence": 4294967293,
      "scriptSigHex": ""
    }
  ],
  "outputs": [
    {
      "value": 50000,
      "scriptPubKeyHex": "00142222222222222222222222222222222222222222"
    },
    {
      "value": 18800,
      "scriptPubKeyHex": "00143333333333333333333333333333333333333333"
    }
  ]
};
const hex = (text) => Buffer.from(text, "hex");
const u32 = (number) => { const out = Buffer.alloc(4); out.writeUInt32LE(number); return out; };
const u64 = (number) => { const out = Buffer.alloc(8); out.writeBigUInt64LE(BigInt(number)); return out; };
const compact = (number) => number < 0xfd ? Buffer.from([number]) : (() => { throw new Error("Bounded example only"); })();
const parts = [u32(project.version), compact(project.inputs.length)];
for (const input of project.inputs) parts.push(Buffer.from(hex(input.txid)).reverse(), u32(input.vout), compact(hex(input.scriptSigHex).length), hex(input.scriptSigHex), u32(input.sequence));
parts.push(compact(project.outputs.length));
for (const output of project.outputs) parts.push(u64(output.value), compact(hex(output.scriptPubKeyHex).length), hex(output.scriptPubKeyHex));
parts.push(u32(project.locktime));
const raw = Buffer.concat(parts);
const txid = Buffer.from(createHash("sha256").update(createHash("sha256").update(raw).digest()).digest()).reverse().toString("hex");
console.log(JSON.stringify({ transactionHex: raw.toString("hex"), txid }, null, 2));
// Expected txid: a71281af068a7276b4b98e5b9c48995c36917019c921b3a12e15a92fb402d267