Top 35+ JavaScript Interview Questions & Answers [2022]

JavaScript, also known as JS, is a server-side programming language. Because JavaScript is extensively used to create various online apps throughout the world, there are several opportunities for JavaScript programming.

You need to pass the JavaScript interview in order to advance in your JavaScript programming careers.

In this article, we have listed down best JavaScript interview questions and answers that are likely to be asked during your job interview. Depending on your expertise and knowledge level, you may be asked basic JavaScript interview questions as well as advanced JavaScript interview questions.

We hope that these JavaScript interview questions will help you to get your dream job as a JavaScript programmer.

Let’s begin:

JavaScript Interview Questions & Answers

1. What is JavaScript, and how does it work?

Ans: JavaScript is a popular client-side and server-side scripting language put into HTML pages Web browsers understand . JavaScript is an Object-Oriented Programming language as well.

2. Can you list down the differences between Java and JavaScript.

Ans: Java is an all-in-one programming environment. JavaScript, on the other hand, is a coded program that may be inserted in HTML pages. These two languages are not at all interdependent and were created with distinct goals in mind.

Java is a client-side scripting language, whereas JavaScript is an object-oriented programming (OOPS) or structured programming languages like C++ or C.

3. What are the different types of data in JavaScript?

Ans: The JavaScript Data types are as follows:

Number
String
Boolean
Object
Undefined.

4. What does the isNaN function do?

Ans: If the argument is not a number, the isNan function returns true; otherwise, it returns false.

5. Which is quicker, JavaScript or an ASP script?

Ans: JavaScript is more efficient and faster. Because JavaScript is a client-side language, it does not require the help of the webserver to run. However, because ASP is a server-side language, it will always be slower than JavaScript. Javascript is now a server-side language as well (NodeJS).

6. What is the definition of negative Infinity?

Ans: In JavaScript, Negative Infinity is a number that may be derived by dividing a negative number by zero.

7. JavaScript was created by which company?

Ans: JavaScript was created by Netscape, a software startup.

8. What is the difference between undeclared and undefined variables?

Ans: Variables that do not exist in a program and are not declared are known as undeclared variables. A runtime error occurs if the program tries to read the value of an undeclared variable.

Undefined variables are variables that have been declared in the program but have yet to be assigned a value. When a program tries to read the value of an undefined variable, it returns an undefined value.

9. What are global variables?

Ans: Global variables are available throughout the code so it has no scope. Declare a local variable or object with the var keyword. A global variable is declared if the var keyword is omitted.

10. What is the purpose of a prompt box?

Ans: A prompt box is a box that provides a text box for the user to enter input. To insert the text or number, a label and box will be presented.

11. In JavaScript, what does the keyword ‘this’ mean?

Ans: ‘This’ keyword refers to the object from where it was called.

12. In JavaScript, how do timers work?

Ans: Timers are used to run a piece of code at a specific time or at a specific interval. The functions setTimeout, setInterval, and clearInterval are used to do this.

13. In Javascript, what symbol is used for comments?

Ans: The following symbols are used:

// for Single line comments and
/* Multi Line Comment */

14. What is the difference between ViewState and SessionState?

Ans: The ‘ViewState’ is unique to each page in a session. ‘SessionState’ refers to user-specific data that may be accessed from any page of a web application.

15. What exactly is the === operator?

Ans: The operator === is known as a strict equality operator since it returns true when the two operands have the same value without being converted.

16. How do you use JavaScript to submit a form?

Ans: You can use JavaScript to submit a form using:

document.form[0].submit();
document.form[0].submit();

17. Does JavaScript support automatic type conversion?

Ans: Automatic type conversion is supported by JavaScript. It is the most frequent type conversion method used by JavaScript developers.

18. How do you use JavaScript to read and write a file?

Ans: Using JavaScript, there are two ways to read and write a file.

Using JavaScript extensions
Using a web page and Active X objects

19. In JavaScript, what are all the looping structures?

Ans: The looping structures in Javascript are as follows:

For
While
Do-while loops.

20. In Javascript, what is variable typing?

Ans: Variable typing is basically used to assign a number to a variable. A string can be allocated to the same variable.

Consider the following scenario:

i = 11;
i = “string;”
This is called variable typing.

21. What would be the result of 5+7+”8″?

Ans: The numbers 5 and 7 will be added numerically because they are both integers. And because 8 is a string, it will be concatenated. As a result, the answer will be 128.

22. In Javascript, what do you mean by NULL?

Ans: The NULL value is used to indicate that there is no value or object. It means that there is no object or null string, as well as no valid boolean value, number, or array object.

23. What is the function of the “delete” operator?

Ans: The delete keyword is used to delete the property and its value.

For example:

var employee= {age:35, batch:”finance”};
Delete employee. age;

24. In JavaScript, what is an undefined value?

Ans: The term “undefined value” refers to something:

The variable that is used in the code does not exist.
The variable is not assigned with any value.
Property doesn’t exist.

25. In JavaScript, what boolean operators are available?

Ans: In JavaScript, the ‘And’ Operator (&&), the ‘Or’ Operator (||), and the ‘Not’ Operator (!) can all be utilized.

26. In JavaScript, what are the several types of pop-up boxes?

Ans: Alert, Confirm, and Prompt are three types of pop-up boxes.

27. What is the use of Void(0)?

Ans: Void(0) is used to prevent the page from getting refreshed, and parameter “zero” is passed while calling.

To call another method without refreshing the page, you have to use Void(0).

28. What’s the difference between a confirmation box and an alert box?

Ans: There is only one button on an alert box, which is the OK button.

A Confirmation box, on the other hand, has two buttons: OK and Cancel.

29. What are JavaScript Cookies and How Do They Work?

Ans: Cookies are small test files that are saved on a computer and are generated when a user visits a website to save information. One of the examples is shopping cart information from previous visits.

30. Does JavaScript has concept level scope?

Ans: No, JavaScript’s concept-level scope isn’t available. The scope of the variable specified inside the function is the function itself.

31. What is the difference between break and continue statements?

Ans: The break statement exits the current loop.

With continue statement, the loop continues with the next statement.

32. What are the different forms of JavaScript errors?

Ans: Errors can be divided into three categories:

Load time errors: Load time errors are errors that appear when a web page is loaded, such as inappropriate syntax errors, and they are generated dynamically.
Runtime errors: Errors that occur as a result of a command being misused inside the HTML language.
Logical Errors: These are errors that occur as a result of incorrect reasoning applied to a function that performs a different operation.

33. In JavaScript, what is the unshift method?

Ans: The unshift method is similar to the push function in that it works at the start of the array. This method is used to prepend one or more elements to the array’s beginning.

34. What exactly is the distinction between JavaScript and Jscript?

Ans: Both are nearly identical. Jscript was developed by Netscape and Microsoft is the creator of JavaScript.

35. Is JavaScript case sensitive?

Ans: Yes, JavaScript is a case-sensitive language.

36. In JavaScript, what is the Document Object Model (DOM)?

Ans: The Document Object Model (DOM) allows JavaScript to access all items on a web page.

37. What is the use of the JavaScript Push method?

Ans: To add or append one or more elements to an Array end, use the push method. By using this method, you can append multiple elements by passing multiple arguments.

Know more about JavaScript.