Javascript Interview Questions

Introduction to Javascript Interview Questions And Answers

With the increase in web-based technologies, it becomes of utmost importance to know an interpreted, high-level programming language besides just HTML and CSS. There are many frameworks present in the market today whose base is JavaScript. If you are planning your career as a front-end web developer, going for JavaScript becomes a mandate. It is an open and cross-platform language that helps in the creation of interactive and dynamic web pages and therefore is quite important. In this post, we have brought you a compilation of JavaScript interview questions and answers, which you should surely find in an interview and helps to raise your bar of understanding to the next level.

So you have finally found your dream job in Javascript but are wondering how to crack the Javascript interview and what could be the probable 2023 Javascript interview questions. Every interview is different, and the scope of a job is different too. Keeping this in mind, we have designed the most common Javascript interview questions and answers to help you get success in your interview.

Below are the top 2023 Javascript Interview Questions which are asked in an interview; these interview questions are divided into two parts are as follows:

Part 1 – Javascript Interview Questions (Basic)

This first part covers basic Javascript interview questions and answers.

1. What is the difference between JavaScript and AngularJS?

Answer:

2. What is the drawback of using a type of bar ===” object” in order to determine if the bar is an object? What measures would you take to avoid this?

Answer:
The above statement can be used to check if a bar is an object, but this poses the problem that even null will also be considered as the object. So the code will log to true instead of false. So, a better way to do this is to apply a check for the null keyword also.

e.g-

print((bar != null) && (typeof bar === "object")); //prints false

3. Why do we wrap the content of the JS file into a single function block?

Answer:
This is done in order to create a closure around file contents, which creates a private namespace and therefore helps in resolving name clashes between modules and libraries.

4. Why do we use “use strict” at the beginning of the JS file?

Answer:
This is the most common Javascript Interview Questions which is frequently asked in a Javascript interview.“use-strict” is a method to enforce strict parsing and error handling at runtime. There could be some code errors that could be ignored, but now they will be thrown explicitly.

5. What is NaN? How do you intend to test the value if it is equal to NaN?

Answer:
NaN represents a value that is not a number. This could be the case when either of the numerator or the denominator value is non-numeric (e.g.- abc/6) or maybe because the result of the operation is non-numeric. You can use isNaN(), but that is not considered as the most reliable way. Another way would be to use abc! =abc and num.isNaN(), which are considered as a more efficient way to test.

Part 2 – Javascript Interview Questions (Advanced)

Let us now have a look at the advanced Javascript Interview Questions

6. What is closure in JavaScript?

Answer:
A closure is referred to as an inner function having access to the variables in the outer function’s scope chain. The closure has access to three scoped variables:

1. Variables in their own scope
2. Variables in the function’s scope
3. Global variables

7. What is function hoisting? What are the two ways of creating a function?

Answer:
In JavaScript, functions and variables are hoisted. The JS interpreter looks forward to finding all the relevant declarations and then hoist them above the function, right where they are declared. There are two ways of creating functions in JavaScript.

1. Function Declaration: It defines the function with the specified parameters.

Syntax:

function name(paramater1, parameter2,…)
{
Statement block
.
.
.
}

Function declarations hoist the definitions, and therefore you can use these functions even before they are declared. This behavior holds valid if your functions are declared inside the global or the functional scope, which is also known as Local Scope in JS. Never use function declarations inside conditional blocks.

2. Function Expression: The keyword “function” is used to define a function within a function.

Syntax:

const myFunc= function [name] (parameter1, parameter2, ….){
[ statements]
}

Where [name] is an optional parameter.

As a result of which these are anonymous functions.

Let us move to the next Javascript interview questions

8. What are the disadvantages of using inner HTML in JavaScript?

Answer.
The use of inner HTML in JavaScript has the following disadvantages:

• When we talk about using inner HTML, it is much slower when compared to the rest of the variables. Its content is slowly built and divided into different elects which takes time to get re-parsed.
• The content gets replaced in JavaScript when we start using inner HTML.
• Appends to inner HTML can’t be used properly.
• Using inner HTML can be used to break the document of JS. As no validation is required, using any type of inner HTML can be a good approach. Broken HTML can pose serious problems.
• The age-old content can be easily replaced.

9. What are screen objects? Define its properties?

Answer:
This is the advanced Javascript Interview Questions asked in an interview. Screen objects are used to read different types of information from a client screen. Properties are as follows:

• A height of the screen is provided.
• Images on the client screen are also provided.
• A width of the screen is provided.
• The height of the client screen includes the taskbar and screen objects give the total height.
• The width of the screen includes the taskbar and the overall width is available to users

10. How does a cookie is read in JS?

Answer:
JS is used to read a cookie. A cookie is just a value of another object which is also termed as the document cookie. This string can be used to get cookies. The same string keeps a tab of the name lists and writing the cookies in different ways such as by using a semicolon. Generally, a cookie is just a single value.

In this Javascript Interview Questions post, we read about some of the most popular and important JavaScript interview questions and answers. Stay tuned to our blog for more posts like these.