Updated June 21, 2023
Introduction to Javascript Interview Questions And Answers
With the increase in web-based technologies, knowing an interpreted, high-level programming language besides HTML and CSS becomes paramount. 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 create 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 find in an interview and helps raise your bar of understanding to the next level.
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 job scope 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.
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:
| JavaScript | AngularJS |
| It is a programing language. | It is primarily a framework for web- and mobile-based applications. |
| It supports programming paradigms such as conditional statements, iterations, exceptions, etc. | It supports iterations or any other conditional constructs. |
| Filters are not supported in JS. | Filters are supported in AngularJS. |
| It is used in building frameworks. | It is built by using JS. |
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 the object. So the code will log to true instead of false. 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 false3. Why do we wrap the content of the JS file into a single function block?
Answer:
This creates a closure around file contents, which makes a private namespace and helps resolve name clashes between modules and libraries.
4. Why do we use “use strict” at the beginning of the JS file?
Answer:
One of the most frequently asked interview questions in a JavaScript interview is about the “use-strict” method. “use-strict” is a way to ensure strict parsing and error handling during runtime. In the past, some code errors could be ignored, but with “use-strict,” these errors are thrown explicitly.
5. What is NaN? How do you intend to test the value if it equals NaN?
Answer:
NaN represents a value that is not a number. This could be the case when either 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(), which is not the most reliable way. Another way would be to use abc! =abc and num.isNaN(), which are considered 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 an inner function accessing the variables in the outer function’s scope chain. The closure has access to three scoped variables:
- Variables in their scope
- Variables in the function’s scope
- Global variables
- What is function hoisting? What are the two ways of creating a role?
Answer:
JavaScript hoists functions and variables. The JS interpreter looks ahead to find all the relevant declarations and then moves them above the function 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; therefore, you can use these functions before they are declared. If your parts are presented within the global or functional scope, also known as the local scope in JS, this behaviour will apply. 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 compared to other variables, using inner HTML is much slower. This is because its content is slowly built and divided into different elements, which takes time to get re-parsed.
- When we start using inner HTML, the content gets replaced in JavaScript. Additionally, it is unsuitable for appending, and using it improperly can break the document of JS.
- Using any inner HTML without validation can pose serious problems, and it can be a bad approach. However, using inner HTML can easily replace age-old content.
9. What are screen objects? Define its properties.
Answer:
Screen objects read different types of information from a client screen. The 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 size of the client screen includes the taskbar, and screen objects give the total length.
- The width of the screen consists of the toolbar, 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 the document cookie. This string can be used to get cookies. The exact line keeps a tab of the name lists and writes 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 essential JavaScript interview questions and answers. Stay tuned to our blog for more posts like these.
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