Questions
3 of 16
1How do you read a file synchronously in Node.js?
2How do you read a file asynchronously in Node.js?
3Explain how to write to a file in Node.js?
4What is the purpose of the `fs.exists()` method in Node.js?
5How can you delete a file in Node.js?
6What is the purpose of the `fs.createReadStream()` and `fs.createWriteStream()` methods in Node.js?
7How can you check if a given path is a file or a directory in Node.js?
8Explain the difference between `fs.readFile()` and `fs.createReadStream()` for reading files in Node.js.
9How can you append data to an existing file in Node.js?
10How can you recursively list all files and directories in a given directory using Node.js?
11What is the purpose of the `fs.mkdir()` method in Node.js, and how can you create directories with it?
12How can you rename a file or directory in Node.js?
13Explain what the `fs.readdir()` method is used for in Node.js.
14What is the purpose of the `fs.rmdir()` method in Node.js, and how can you delete a directory with it?
15What is the difference between `fs.unlink()` and `fs.unlinkSync()` in Node.js?
16How can you watch for file changes in a directory using Node.js?
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03 / 16

Explain how to write to a file in Node.js?

You can write to a file in Node.js using the fs.writeFile() method. Here's an example:

javascript
Difficulty: 2/10
Topics: fs module, async vs sync, streams

Scenario Questions

0-2 years experience
  1. 1

    How would you write a JSON config object to a file called config.json?

  2. 2

    What happens if you call fs.writeFile on a path that's actually a directory?

  3. 3

    Why might you use writeFileSync in a CLI startup script instead of the async version?

2-5 years experience
  1. 1

    You're adding a request logger that appends to a file. The app crashes and the last few log lines are missing. What went wrong?

  2. 2

    A teammate used fs.writeFileSync inside an Express route handler. Why is that problematic under load?

  3. 3

    How would you implement atomic writes so a reader never sees a half-written file?

5-8 years experience
  1. 1

    Design a file-based cache that handles concurrent writes from multiple worker processes without corruption.

  2. 2

    Your service streams large CSV exports to disk. Users report memory spikes during export. How do you fix it?

  3. 3

    How would you implement log rotation (daily files, max 30 days) without losing log entries during the rotation moment?

8+ years experience
  1. 1

    We're migrating from local filesystem writes to S3. How do you design the abstraction layer so callers don't change?

  2. 2

    Multiple services write to a shared NFS mount. How do you prevent corruption and ensure consistency?

  3. 3

    Design a write-ahead log for a custom embedded database engine — durability, recovery, and compaction.

Follow-up Questions

  • ❓What happens if the file doesn't exist?
  • ❓How would you handle writing a 10GB file?
  • ❓When would you choose sync over async?