Question 1

How do parameter properties work?

Accepted Answer

Constructor parameter shortcuts like public readonly id: string auto-create fields. Concise for DTOs/services. Don't overuse for fat constructors.

Question 2

public/private/protected vs #private?

Accepted Answer

TS visibility is compile-time; # is runtime private hard privacy. private can be bypassed via brackets; # cannot. Choose based on encapsulation needs.

Question 3

abstract classes vs interfaces?

Accepted Answer

Abstract classes can provide implementation + template methods; interfaces are pure contracts. Use abstract when sharing code; interfaces when multiple unrelated implementers.

Question 4

What does implements do?

Accepted Answer

Requires a class to satisfy an interface's members structurally. Doesn't add runtime. Excess property nuances differ from object literals.

Question 5

Class field initialization order pitfalls?

Accepted Answer

Base fields/constructors vs derived; use definite assignment and careful supers. TS definite assignment assertions (!) can hide bugs — prefer proper init.

Question 6

When are classes preferable to closures/factories?

Accepted Answer

When you need instanceof, inheritance hierarchies, or DI frameworks expecting classes. Otherwise functions + modules often simpler. Prefer composition.

Question 7

Typing this in class methods/callbacks?

Accepted Answer

Arrow properties capture this; bind; or specify this parameters. Passing raw methods as callbacks loses this — classic bug.

Classes TypeScript Interview Questions

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