JavaScript and Node.js: Streaming Decisions

Understand the idea

Install a current Node.js release. A Node program can use built-in readline to process the adapter's stdin one line at a time. JavaScript objects map directly to JSON objects. Keep the choice function synchronous unless you truly need asynchronous data; the adapter has a 20-second response wait.

Use optional chaining for missing fields, booleans for legal flags, and process.stderr for diagnostics. The program below requires no package and can be launched as node bot.mjs through FLAWLESS_BOT_COMMAND.

import readline from 'node:readline';

function choose(obs) {
  const legal = obs?.legal ?? {};
  if (legal.check) return { kind: 'check' };
  if (legal.call && legal.callAmount <= 20) return { kind: 'call' };
  if (legal.fold) return { kind: 'fold' };
  throw new Error('No supported legal action');
}

for await (const line of readline.createInterface({ input: process.stdin })) {
  try {
    process.stdout.write(JSON.stringify(choose(JSON.parse(line))) + '\n');
  } catch (error) {
    console.error('Observation error:', error);
    process.stdout.write('{"kind":"fold"}\n');
  }
}