Javascript interview questions and answers

JavaScript Interview questions
and answers

1. What is JavaScript?
JavaScript is a scripting language with the
OOPs( object-oriented language )
capability. It is used to create dynamic
pages but nowadays JavaScript is also
as a server-side scripting language.

2. How to add JavaScript in an
HTML file?
We use a script tag to add a
JavaScript file in an HTML file.
for example:-
<script src=“filename.js”></script>

3. What is the use of the typeof
operator?
To check the type of variable in
JavaScript we use the typeof
operator.

4. Difference between null and
undefined in JavaScript.
Null: The value of the variable is
purposely absent.
undefined: the value of the variable
does not exist in Program.

5. What is the use of isNaN?
isNaN( is Not a Number ) is
used to check whether a
is a number or not. If the
value is a number then it
returns false otherwise it
returns true.

6. Disadvantages of using
JavaScript?
Client-side JavaScript does not
allow us to read or write data in
files. Because of security reasons.
Also, JavaScript doesn't support
multithreading.

7. What is the "this" keyword in
JavaScript?
JavaScript is more famous for the
"this" keyword. "this" keyword
to the object where it was

8. What is the difference between
== and === operator?
== operator compare the value of
two operands but === operator
compares the value as well as the
type of operands.

9. What is BOM?
BOM stands for Browser Object
Model. Using it we can interact
with Browser.

10. What is DOM?
DOM stands for Document
Object Model. Using it we can
manipulate HTML files.

Thank You
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Javascript interview questions and answers

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