Node.js Mastery: Challenging Interview Questions for 2025 Quiz

1. 1. Deep Event Loop Understanding

   In a Node.js application, what happens if a long-running CPU-bound computation runs directly on the main thread? For example, if a for-loop runs for several seconds synchronously.

   1. A. Node.js will continue processing other client requests as usual.
   2. B. The Event Loop will be blocked, causing the application to become unresponsive.
   3. C. Node.js will automatically delegate the computation to a worker thread.
   4. D. An out-of-memory exception will be thrown immediately.
   5. E. The computation will be split into smaller asynchronous tasks automatically.

2. 2. Core Modules Identification

   Which of the following is NOT a built-in Node.js core module? For example, consider importing modules without external installation.

   1. A. http
   2. B. fs
   3. C. path
   4. D. express
   5. E. crypto

3. 3. Stream API Complexity

   Given a large file, what is the main benefit of using Node.js streams to read and process it compared to fs.readFile()? For instance, processing a 10GB log file.

   1. A. Streams read the entire file into memory at once, making processing faster.
   2. B. Streams allow for processing data in chunks, reducing memory usage.
   3. C. Streams automatically compress the file while reading.
   4. D. fs.readFile is faster and more memory-efficient than streams.
   5. E. Streams only work with text files.

4. 4. Cluster Module Subtleties

   What is the primary purpose of the cluster module in Node.js? For example, when building a web server handling thousands of concurrent users.

   1. A. To automatically balance HTTP requests across remote servers.
   2. B. To utilize multiple CPU cores by spawning child processes.
   3. C. To enable asynchronous I/O operations within a single thread.
   4. D. To reload code when changes are detected.
   5. E. To manage package dependencies between modules.

5. 5. Asynchronous Patterns

   Which of the following is the correct way to promisify a Node.js callback-based API? For example, converting fs.readFile to return a Promise.

   1. A. fs.readFileAsync(path)
   2. B. require('util').promisify(fs.readFile)
   3. C. fs.promisifyRead(path)
   4. D. readFile.promised(path)
   5. E. fs.promise.readFile(path)

6. 6. Error Event Handling

   What happens if an 'error' event emitted by a Node.js stream is not handled? For example, a readable stream that encounters a file read error.

   1. A. The process ignores the error silently.
   2. B. The error is automatically logged and the stream continues.
   3. C. The process crashes with an uncaught exception.
   4. D. The stream retries reading the file automatically.
   5. E. The error event is converted to a warning.

7. 7. NPM Dependency Versioning

   If a package.json lists a dependency as ^1.5.3, which of the following versions could NPM install? For example, when running npm install.

   1. A. 1.4.9
   2. B. 2.0.0
   3. C. 1.6.0
   4. D. 0.9.0
   5. E. 1.5.2

8. 8. Process.nextTick Nuances

   What is the function of process.nextTick() in the Node.js event loop? For example, when scheduling a callback after the current operation completes.

   1. A. It schedules a task immediately after I/O events.
   2. B. It schedules a task to execute at the start of the next Event Loop iteration.
   3. C. It schedules a task before any other asynchronous tasks, after the current operation.
   4. D. It is equivalent to setTimeout(fn, 0).
   5. E. It delays execution until all network I/O is finished.

9. 9. OS Module Subtleties

   Which method from the Node.js 'os' module returns the system uptime in seconds? For example, to print how long the system has been running since the last reboot.

   1. A. os.platform()
   2. B. os.sysUptime()
   3. C. os.uptime()
   4. D. os.time()
   5. E. os.tick()

10. 10. Secure Coding Practices

    Which of the following is the most secure way to prevent prototype pollution attacks when parsing JSON data in a Node.js application?

    1. A. Using JSON.parse() without any validation.
    2. B. Deleting __proto__ property after parsing.
    3. C. Validating incoming keys against an allowed whitelist before parsing.
    4. D. Using eval() to parse JSON after replacing dangerous keys.
    5. E. Converting the JSON to a string and back repeatedly.