Reading Files in Node.js Interview Questions

Q1. How do you read a file asynchronously in Node.js?

Use fs.readFile() with a callback. Example:

const fs = require('fs');

fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) {
    console.error(err);
    return;
  }
  console.log(data);
});

The 'utf8' encoding returns the file content as a string. Without encoding, it returns a buffer. Always handle errors properly.

Q2. How do you read a file synchronously?

Use fs.readFileSync(). Example:

try {
  const data = fs.readFileSync('example.txt', 'utf8');
  console.log(data);
} catch (err) {
  console.error(err);
}

Synchronous methods block the event loop, so they're not recommended for production servers handling many requests. They're okay for initialization scripts or CLI tools.

Q3. How do you read a file using promises?

Use fs.promises.readFile(). Example:

const fs = require('fs').promises;

async function readFile() {
  try {
    const data = await fs.readFile('example.txt', 'utf8');
    console.log(data);
  } catch (err) {
    console.error(err);
  }
}

This combines the benefits of async operations with cleaner syntax using async/await.

Q4. How do you read large files efficiently?

For large files, use streams: fs.createReadStream(). This reads the file in chunks without loading the entire file into memory. Example:

const readStream = fs.createReadStream('largefile.txt', 'utf8');

readStream.on('data', (chunk) => {
  processChunk(chunk);
});

readStream.on('end', () => {
  console.log('Done');
});

Q5. How do you handle different encodings when reading files?

You can specify encoding as the second argument: 'utf8', 'ascii', 'base64', 'hex', etc. If you need to handle binary data, omit encoding to get a buffer. You can also specify encoding in the options object:

fs.readFile('file.txt', { encoding: 'utf8', flag: 'r' }, callback);

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