MEAN Stack Development 5

Question 1

In Angular, what is the difference between `Observable` and `Promise`?

Accepted Answer

Observables are lazy and can emit multiple values over time; Promises resolve once

Answer

Observables from RxJS are lazy streams that can emit multiple values and be cancelled, whereas Promises eagerly resolve to a single value.

Question 2

What is the purpose of MongoDB indexes, and what is the trade-off of adding too many?

Accepted Answer

Indexes speed up query performance; too many slow down write operations

Answer

Indexes dramatically speed up read queries by allowing MongoDB to avoid full collection scans, but each index must be updated on every write, increasing write overhead.

Question 3

Which Angular CLI command generates a new service called `data`?

Accepted Answer

ng generate service data

Answer

`ng generate service data` (or `ng g s data`) creates a new service file with the @Injectable decorator pre-configured.

Question 4

In Express.js, how do you access JSON data sent in a POST request body?

Accepted Answer

req.body (after using express.json() middleware)

Answer

After applying the express.json() middleware, parsed JSON from the request body is available on req.body.

Question 5

What does the Mongoose `populate()` method do?

Accepted Answer

Replaces ObjectId references with the actual referenced documents

Answer

populate() automatically replaces ObjectId reference fields with the full document data from the referenced collection, similar to a JOIN.

MEAN - Stack Development Practice Test

MEAN - Stack Development Practice Test

MEAN Stack Development 5