It is essential to have a full understanding of Javascript if you want to start your career in the IT industry.
The article introduces the top 20 Javascript interview questions, which are most likely to be asked during an interview.
The Top 20 Javascript Interview Questions
1. What is JavaScript?
ANS: Netscape created the javascript scripting language. It's possible to program web browsers or even servers with it. The benefit of this language is that it can dynamically update the contents of a webpage.
2. What are JavaScript datatypes?
ANS: Primitive data types and Non-primitive data types are the two basic types of data types in JavaScript.
Number, String, Boolean, Undefined, Null, and Symbol are primitive data types in Javascript.
Non-primitive datatypes, on the other hand, include objects in Javascript.
3. Explain 'this' keyword in JavaScript.
ANS: In Javascript, the keyword refers to a specific object. It refers to the thing to which it belongs. How a function is invoked determines the object. The keyword ‘this' appears in the function that is called.
4. What is DOM?
ANS: The Document Object Model (DOM) is an acronym for Document Object Model. The logical structure of a document is defined by the DOM. The Document Object Model (DOM) also explains how a document can be accessed and changed.
5.Explain the '===' operator?
ANS: In Javascript, the ‘===’ operator is a strict equality comparison operator. This operator returns false if the values are not of a similar type. For example, if 2 and “2” are compared with ‘===’ then it would return false because the types of both the values are different.
6. What are the advantages of JavaScript?
ANS: It is lightweight and simple to install. It uses a minimal amount of memory.
It is a language that is interpreted. Instructions are carried out immediately.
It is an object-oriented programming language.
First-class functions: A function can be used as a value in JavaScript.
Scripting Language: It's a programming language that allows you to write instructions for a run-time environment.
7. What is the use of the isNaN function?
ANS:isNan function returns true if the argument is not a number; otherwise, it is false
8. Which symbol is used for comments in Javascript?
ANS:// for Single line comments and
/* Multi
Line
Comment
*/
9. What are all the looping structures in JavaScript?
ANS: Following are looping structures in Javascript:
For
While
Do-while loops
10. What would be the result of 3+2+”7″?
ANS: Since 3 and 2 are integers, they will be added numerically. And since 7 is a string, its concatenation will be done. So the result would be 57.
11. How do you create an array in JavaScript?
ANS: Here is a very simple way of creating arrays in JavaScript using the array literal:
var a = [];
var b = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’];
12. How do you create an object in JavaScript?
ANS: Since JavaScript is essentially an object-oriented scripting language, it supports and encourages the usage of objects while developing web applications.
const student = {
name: 'John',
age: 17
}
13. Explain String in JavaScript?
ANS: The group of character or textual data is called string, in JavaScript, there is no separate type for the character, even a single character will be stored as a string. In JavaScript, the string can be enclosed with single quotes or double quotes
var str = 'hello';
console.log(str);//print hello
14. Is JavaScript a case-sensitive language?
ANS: Yes, JavaScript is a case-sensitive language. The language keywords, variables, function names, and any other identifiers must always be typed with a consistent capitalization of letters.
15. What is Callback?
ANS: A callback is a simple JavaScript function that is supplied as an argument or option to a method. The name "call back" refers to a function that is called after another function has completed its execution. Functions are objects in JavaScript. As a result, functions can accept functions as arguments and return them to other functions.
16. What is Closure?
ANS: When a variable defined outside the current scope is accessed from within another scope, a closure is produced. It allows you to access the scope of an outer function from within an inner function. Closures are created every time a function is created in JavaScript. Simply write a function within another function and expose it to use a closure.
17. How to create a cookie using JavaScript?
ANS:The simplest way to create a cookie is to assign a string value to the document.cookie object
SYNTAX - document.cookie = "key1 = value1; key2 = value2; expires = date";
18. In how many ways a JavaScript code can be involved in an HTML file?
ANS: A JavaScript code can be included in an HTML file in three different ways. They are:
19. What is a Typed language?
ANS: Typed Language is in which the values are associated with values and not with variables.
20. What is negative Infinity?
ANS: Negative Infinity is a number in JavaScript that can be derived by dividing negative numbers by zero.