Back-End Development Development 3

Question 1

In Node.js, what mechanism allows non-blocking I/O operations despite JavaScript being single-threaded?

Accepted Answer

The event loop and libuv async I/O library

Answer

Node.js delegates I/O to libuv, which uses OS-level async mechanisms, and the event loop picks up callbacks when operations complete.

Question 2

What SQL clause is used to filter groups produced by GROUP BY?

Accepted Answer

HAVING

Answer

HAVING filters aggregated groups after GROUP BY, whereas WHERE filters rows before aggregation.

Question 3

Which caching strategy writes data to the cache and the database simultaneously on every write?

Accepted Answer

Write-through

Answer

Write-through ensures the cache and database are always in sync by writing to both on every update, at the cost of higher write latency.

Question 4

What does CORS stand for, and why do browsers enforce it?

Accepted Answer

Cross-Origin Resource Sharing; browsers enforce it to prevent unauthorized cross-origin requests

Answer

CORS is a security mechanism that restricts web pages from making requests to a different origin than the one that served the page.

Question 5

Which index type is most efficient for equality lookups on low-cardinality columns in a relational database?

Accepted Answer

Bitmap index

Answer

Bitmap indexes are highly efficient for low-cardinality columns (e.g., gender, status) because they represent values as bit arrays enabling fast bitwise operations.

Back-End Development Practice Test

Back-End Development Practice Test

Back-End Development Development 3