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8 questions on OOP & Classes. Pass 70% to clear the chapter.

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TS OOP & Classes — Chapter Quiz

Eight questions on classes, modifiers, abstract, decorators, enums, and namespaces.

0/ 8

Question 1
1
What's the difference between TS private and JS #field?
ANo differenceBTS private is compile-time only; #field is real runtime privacyC#field is slowerD#field is older
TS private is erased at compile time — accessible from JS. #field is a real JS feature with runtime privacy.
Question 2
2
What does implements do?
AInherits implementation from a parent classBAsserts that a class conforms to an interfaceCImports a moduleDDefines an abstract method
implements is a shape check — it asserts the class satisfies one or more interfaces. It doesn't inject code.
Question 3
3
An abstract class can be instantiated directly with new.
TTrueFFalse
Abstract classes can't be new-ed. They must be subclassed, and the subclass must implement all abstract members.
Question 4
4
What's special about this constructor parameter?
```
class Point {
  constructor(public x: number, public y: number) {}
}
```
ANothing — just type annotationsBpublic creates and assigns the field automaticallyCIt makes them read-onlyDIt throws an error
Adding a modifier (public / private / readonly) on a constructor parameter is a "parameter property" — TS declares and assigns the field for you.
Question 5
5
Which is the modern TypeScript-recommended replacement for enum?
AA union of string literalsBA classCAn interfaceDA namespace
type LogLevel = "debug" | "info" | "warn" — zero runtime cost, same compile-time safety. Or as const on an object literal.
Question 6
6
An accessor that lets callers read a derived property without parens is called a ___.
get name() { ... } declares a getter. Callers write obj.name, not obj.name().
Question 7
7
Which keyword marks a class member as accessible to subclasses but not outside the class hierarchy?
ApublicBprivateCprotectedDinternal
protected allows access from the declaring class and any subclasses, but not from outside.
Question 8
8
What is the modern (Stage 3) decorator syntax used for?
AAdding CSS classesBFunctions that modify classes, methods, or fields at definition timeCAnnotating typesDRenaming variables
Decorators are functions that run at class definition time to wrap or modify members. Common in NestJS, TypeORM, etc.