Weak Areas

Question 1

What is a closure in JavaScript?

Answer 1

A closure is when a function remembers and can access variables from its outer scope even after that outer function has finished executing.

Question 2

What is memoization used for?

Answer 2

Memoization is used to speed up functions by caching the results of expensive function calls and returning the cached result when the same input occurs again.

Question 3

How does memoization typically use closures?

Answer 3

Memoization uses closures to maintain a private cache object that persists across calls to the memoized function.

Question 4

What is Object-Oriented Programming (OOP) in JavaScript?

Answer 4

A programming paradigm based on objects and classes to model real-world things using properties and methods.

Question 5

What are the four main principles of OOP?

Answer 5

Encapsulation

Question 6

What is encapsulation?

Answer 6

Hiding the internal details of an object and exposing only what is necessary through public methods.

Question 7

What is abstraction?

Answer 7

Hiding complex implementation details and showing only the necessary features of an object.

Question 8

What is inheritance in JavaScript?

Answer 8

A mechanism where one object can acquire properties and methods from another object.

Question 9

What is polymorphism?

Answer 9

The ability of different objects to be accessed through the same interface

Question 10

How do you create an object in JavaScript?

Answer 10

Using object literals {}

Question 11

What is a class in JavaScript?

Answer 11

A blueprint for creating objects with shared properties and methods introduced in ES6.

Question 12

How do you define a class in JavaScript?

Answer 12

Using the ‘class’ keyword, followed by the class name and a constructor method.

Question 13

What is a constructor method?

Answer 13

A special method used for initializing new objects created from a class.

Question 14

How do you create an instance of a class?

Answer 14

Using the ‘new’ keyword followed by the class name.

Question 15

What is the ‘this’ keyword in JavaScript?

Answer 15

Refers to the current object instance within a method.

Question 16

What is method overriding?

Answer 16

Providing a new implementation of a method inherited from a parent class.

Question 17

What is a prototype in JavaScript?

Answer 17

An object from which other objects inherit properties and methods.

Question 18

What is the prototype chain?

Answer 18

A mechanism where objects inherit from other objects

Question 19

How does JavaScript handle inheritance?

Answer 19

Through prototypes and the prototype chain.

Question 20

What is the difference between class-based and prototype-based OOP?

Answer 20

Class-based uses classes and instances; prototype-based uses objects and their prototypes directly.

Question 21

Can you modify a prototype?

Answer 21

Yes

Question 22

What is the benefit of using prototypes?

Answer 22

It allows sharing methods across all instances

Question 23

How can you achieve encapsulation in JavaScript?

Answer 23

Using closures or the new private fields (#) syntax inside classes.

Question 24

What are private fields in JavaScript classes?

Answer 24

Properties prefixed with # that cannot be accessed outside the class.

Question 25

What is static method in JavaScript?

Answer 25

A method defined on the class itself

Question 26

How do you define a static method?

Answer 26

Using the 'static' keyword inside the class.

Question 27

What is the difference between 'instance method' and 'static method'?

Answer 27

Instance methods are called on objects; static methods are called on the class itself.

Question 28

What is super() in JavaScript?

Answer 28

A method to call the parent class constructor from a child class constructor.

Question 29

What is the difference between 'object' and 'class' in JavaScript?

Answer 29

An object is an instance; a class is a blueprint to create instances.

Question 30

What is duck typing in JavaScript?

Answer 30

A concept where an object's suitability is determined by the presence of certain methods and properties rather than the object's type.

Question 31

What is composition vs inheritance?

Answer 31

Composition combines simple objects to build complex ones; inheritance derives new objects from existing ones.

Question 32

When should you prefer composition over inheritance?

Answer 32

When you want more flexibility and to avoid deep inheritance hierarchies.