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What are 'Event Emitting' patterns and how does error-first callback convention relate to them?

Q: What are 'Event Emitting' patterns and how does error-first callback convention relate to them?

**TL;DR.** Node has two async patterns. **Error-first callbacks** (( err, result ) as the last argument) suit **one-shot** operations like reading a file. **Event emitting** ( EventEmitter ) suits **repeated/streamed** results — many 'data' events plus terminal 'end' / 'error' events. They share one rule: **errors are explicit**, either as the first callback arg or a dedicated 'error' event. error-first callback fn(args, (err, res) => …) one result, then done error

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Asks the candidate to compare two fundamental asynchronous patterns in Node.js.

asyncpatternsevents

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Both conventions side by side

// Error-first callback: one result
fs.readFile('a.txt', (err, data) => {
  if (err) return console.error(err);
  console.log(data.toString());
});

// EventEmitter/stream: many results + terminal events
const rs = fs.createReadStream('big.txt');
rs.on('data', (chunk) => process(chunk));
rs.on('error', (err) => console.error(err));   // required
rs.on('end', () => console.log('done'));

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