MCQs on Classes and Object-Oriented Features | TypeScript

200+ FREE TypeScript Basics MCQs Quiz | MCQs on TypeScript MCQs on Classes and Object-Oriented Features | TypeScript

Deep dive into TypeScript’s object-oriented features with 30 MCQs focused on Classes, Constructors, Access Modifiers, Readonly Properties, Getters/Setters, and Static Members. Boost your TypeScript OOP skills!

Chapter 7: Classes and Object-Oriented Features

Classes and Constructors

In TypeScript, how do you declare a class?
- a) class ClassName { }
- b) function ClassName { }
- c) object ClassName { }
- d) class: ClassName { }
How do you define a constructor method in TypeScript?
- a) constructor() { }
- b) class constructor() { }
- c) init() { }
- d) constructorFunction() { }
What keyword is used to create an instance of a class in TypeScript?
- a) create
- b) new
- c) this
- d) instance
How do you call the constructor of a class in TypeScript?
- a) By using the new keyword
- b) By directly calling the constructor name
- c) By using the call() function
- d) By defining the constructor function again
In TypeScript, how would you define a class with a constructor that accepts two arguments?
- a) class Person { constructor(name, age) { } }
- b) class Person { constructor(name: string, age: number) { } }
- c) class Person(name: string, age: number) { }
- d) class Person { name: string, age: number; constructor() { } }

Public, Private, and Protected Access Modifiers

Which access modifier makes a class member accessible everywhere, both inside and outside the class?
- a) private
- b) public
- c) protected
- d) readonly
What does the private access modifier do in TypeScript?
- a) Makes the member accessible only within the class
- b) Makes the member accessible inside and outside the class
- c) Makes the member accessible in child classes only
- d) Makes the member read-only
Which modifier allows access to a class member only within the class and its subclasses?
- a) private
- b) public
- c) protected
- d) readonly
Can a private member of a class be accessed outside the class in TypeScript?
- a) Yes, through a getter function
- b) Yes, using reflection
- c) No, it is completely inaccessible
- d) Yes, if the class is extended
Which of the following will result in a compilation error?
- a) class Person { public name: string; }
- b) class Person { private name: string; }
- c) class Person { protected name: string; }
- d) class Person { name: string; }

Readonly Properties

What does the readonly modifier do in TypeScript?
- a) Makes the property immutable after initialization
- b) Allows the property to be modified only within the class
- c) Prevents the class from being inherited
- d) Makes the property accessible only within the constructor
How do you declare a readonly property in TypeScript?
- a) readonly name: string;
- b) const name: string;
- c) static readonly name: string;
- d) let readonly name: string;
Can a readonly property be modified after initialization?
- a) Yes, if declared as static readonly
- b) Yes, but only inside the constructor
- c) No, it cannot be modified
- d) Yes, if accessed via a setter
Can a readonly property be assigned to a new value inside a method?
- a) Yes, using a setter method
- b) Yes, but only in the constructor
- c) No, it cannot be reassigned
- d) Yes, using direct property assignment
Which of the following will result in a compilation error?
- a) readonly age: number;
- b) readonly name: string = "John";
- c) readonly name: string; name = "John";
- d) readonly name: string = "Alice";

Getters and Setters

What is the purpose of a getter method in TypeScript?
- a) To modify the value of a property
- b) To return the value of a property
- c) To validate the value of a property
- d) To restrict access to a property
What keyword is used to define a getter method in TypeScript?
- a) get
- b) setter
- c) access
- d) return
Which of the following is the correct syntax for defining a getter method in a class?
- a) get age() { return this._age; }
- b) getter age() { return this._age; }
- c) get age: number { return this._age; }
- d) get return age { return this._age; }
What is the purpose of a setter method in TypeScript?
- a) To prevent access to a property
- b) To validate or modify the value of a property
- c) To define the initial value of a property
- d) To create a constant property
How do you define a setter method in TypeScript?
- a) set property(value: string) { this._property = value; }
- b) setter property(value: string) { this._property = value; }
- c) set property = (value: string) { this._property = value; }
- d) set property(value: string): void { this._property = value; }
Can a class have both getter and setter methods for the same property?
- a) Yes, but only for private properties
- b) No, only one can exist
- c) Yes, you can have both
- d) Only for readonly properties
Which of the following is true about getters and setters in TypeScript?
- a) They can be accessed as regular properties
- b) They must be manually invoked
- c) Getters and setters must return void
- d) Setters can only return a string

Static Members

What does a static member in a class mean in TypeScript?
- a) It can only be accessed by instances of the class
- b) It is shared among all instances of the class
- c) It can only be accessed from outside the class
- d) It can only be accessed in the constructor
How do you declare a static property in TypeScript?
- a) static property: string;
- b) static string property;
- c) property static string;
- d) string static property;
Can static methods access instance properties in TypeScript?
- a) Yes, through the this keyword
- b) No, they cannot access instance properties
- c) Yes, but only with inheritance
- d) Yes, if declared inside the constructor
How do you call a static method in TypeScript?
- a) instance.method();
- b) ClassName.method();
- c) this.method();
- d) Class.method();
Which of the following is true for static methods?
- a) They are bound to instances of the class
- b) They can be called without creating an instance of the class
- c) They cannot be inherited
- d) They are not part of the class
Can static properties be accessed using this in a non-static method?
- a) Yes, without issues
- b) No, it results in a compile-time error
- c) Yes, but only inside the constructor
- d) Yes, using the super keyword
What is the advantage of using static members in a class?
- a) They reduce memory usage by not duplicating data in instances
- b) They help create private properties
- c) They ensure that every instance has a unique copy of the property
- d) They improve the performance of instance methods
What happens if you try to access a non-static method with ClassName.method();?
- a) The method will execute normally
- b) TypeScript will throw an error
- c) The method will be automatically converted to static
- d) It will return undefined

Answer Key

Qno	Answer
1	a) class ClassName { }
2	a) constructor() { }
3	b) new
4	a) By using the `new` keyword
5	b) class Person { constructor(name: string, age: number) { } }
6	b) public
7	a) Makes the member accessible only within the class
8	c) protected
9	c) No, it is completely inaccessible
10	c) class Person { protected name: string; }
11	a) Makes the property immutable after initialization
12	a) readonly name: string;
13	c) No, it cannot be modified
14	c) No, it cannot be reassigned
15	c) readonly name: string; name = “John”;
16	b) To return the value of a property
17	a) get
18	a) get age() { return this._age; }
19	b) To validate or modify the value of a property
20	a) set property(value: string) { this._property = value; }
21	c) Yes, you can have both
22	a) They can be accessed as regular properties
23	b) It is shared among all instances of the class
24	a) static property: string;
25	b) No, they cannot access instance properties
26	b) ClassName.method();
27	b) They can be called without creating an instance of the class
28	b) No, it results in a compile-time error
29	a) They reduce memory usage by not duplicating data in instances
30	b) TypeScript will throw an error

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