Explain JS types, Promises, Maps, WebSockets

Q: Explain JS types, Promises, Maps, WebSockets

This is a Other / Miscellaneous interview question from Citadel for Software Engineer roles. View the full question and solution on PracHub.

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Question

JavaScript Types, Promises, Collections, and WebSocket Ordering

You are interviewing for a software engineering role. Answer the following about JavaScript runtime behavior, collections, and networking:

1) Data Types and Data Structures

List JavaScript primitive types vs reference types.
Name common built-in data structures used in practice.
Which values coerce to false in a boolean context?

2) Promises: Return Values and Error Propagation

What do then / catch / finally return?
What happens if an error is thrown in the Promise executor or in any handler (including inside an async function)?

3) Plain Objects vs Map

Compare by:

Key types allowed
Iteration order
Default/inherited properties and collision issues
Performance characteristics (adds/removes/lookups)
Typical use cases

4) WeakMap

What is it?
How do its key constraints and garbage-collection behavior differ from Map ?

5) WebSockets and Message Ordering

Does a single WebSocket connection guarantee in-order, reliable delivery?
When can ordering be affected (e.g., multiple connections, reconnections, server fan-out)?
How would you design for ordering and/or idempotency if required?