JavaScript

Question 1

What is a Promise?

Answer 1

An object that allows a function to handle asynchronous operations (like fetching data)

Question 2

What is DOM manipulation?

Answer 2

When JavaScript is used to add, remove, and modify HTML elements.

Question 3

What are the 5 primitive data types in JavaScript?

Answer 3

A primitive is a data type that isn’t composed of other data types. They are:
* Boolean
* Undefined
* Null
* Number
* String

Question 4

How is the this keyword used?

Answer 4

The this keyword refers to the object that the function is a property of.

Question 5

What is hoisting?

Answer 5

The default behaviour of JavaScript, where all the variable and function declarations are moved to the top of the file during runtime.

Question 6

What is a higher order function?

Answer 6

Functions that either (1) take other as arguments or (2) returns other functions.

Question 7

What is a closure?

Answer 7

It’s an ability of a function to remember the variables and functions that are declared in its outer scope.

Question 8

How can OOP be implemented in JavaScript?

Answer 8

OOP is a programming style where functions and variables are organised in objects. It can be implemented in JavaScript through regular objects or classes.

Question 9

What is the difference between var, let and const keywords?

Answer 9

• Scope
  
  • “var” is scoped to the function in which they are created, or if created outside of any function, to the global object. “
  • let” and “const” are block scoped, meaning they are only accessible within the nearest set of curly braces (function, if-else block, or for-loop).
• Hoisting
  
  • “var” is hoisted and initialized at runtime
  • “let” and “const” are hoisted but not initialized at runtime.
• Assignment
  
  • “var” and “let” can be reassigned
  • “const” cannot be reassigned

Question 10

What does pass by reference or pass by value mean?

Answer 10

• Primitive data types (like numbers, strings or booleans) are passed by value.
• Non-primitive data types (like objects or arrays) are passed by reference.

Question 11

What is prototypal inheritance?

Answer 11

All JavaScript objects have a __proto__ property (with the exception of objects created with Object.create(null)). This __proto__ is a reference to another object, which is called the object’s “prototype”.

When a property is accessed on an object and if the property is not found on that object, it will go down the “prototypal chain” until it finds the original prototype.