(2023)-Top JavaScript Interview Questions and Answers

1 .

JavaScript is the programming language of the Web. Javascript Most commonly used websites this is client-side script to interact with the user and make dynamic pages. All modern web browsers on desktops, tablets, and smart phones are using JavaScript.

2 .

Which company developed JavaScript ?

The first JavaScript engine was created by Brendan Eich at Netscape, for the Netscape Navigator Web browser. The engine, code-named SpiderMonkey, is implemented in C. It has since been updated (in JavaScript 1.5) to conform to ECMAScript 3.

3 .

How to create function in JavaScript ?

To create function in JavaScript, follow the following syntax :

function function_name(){

//function body

}

</script>

4 .

What is Javascript Variables ?

JavaScript uses reserved keyword var to declare a variable. A variable must have a unique name. You can assign a value to a variable using equal to (=) operator when you declare it or before using it.

There are two types of variables in JavaScript :

1. local variables : A variable that is declared inside of a function definition is called local variable and has scope to that function only.

2.global variables : A variable that is declared outside of a function definition is called a global variable and its scope is throughout your program means its value is accessible and modifiable throughout your program.

Basic Syntax :

var <variable-name>;

var <variable-name> = <value>;

5 .

How many Operators in Javascript ?

JavaScript operators are used to assign values, compare values, arithmetic operations, and more. For example 1 + 2, where + sign is an operator and 1 is left operand and 2 is right operand. + operator adds two numeric values and produces a result which is 3 in this case.

1. Arithmetic Operators

2. Comparison Operators

3. Logical Operators

4. Bitwise Operators

5. Assignment Operators

6 .

What are JavaScript Data Types ?

Following are the JavaScript Data types :

1. Primitive data type

2. Non-primitive (reference) data type

JavaScript has dynamic types. This means that the same variable can be used to hold different data types :

var x; // Now x is undefined

var x = 10; // Now x is a Number

var x = "Name"; // Now x is a String

Primitive data types : There are six types of primitive data types in JavaScript. They are as follows :

Number

String

Boolean

Null

Symbol

Undefined

Non-Primitive data types : The non-primitive data types are as follows :

Object

Array

RegExp

7 .

What is a prompt box ?

A prompt box is a box which allows the user to enter input by providing a text box. Label and box will be provided to enter the text or number.

8 .

What is ‘this’ keyword in JavaScript ?

‘this’ keyword refers to the object from where it was called.

9 .

What is the difference between == and === ?

The == operator checks equality only whereas === checks equality and data type i.e. value must be of same type.

10 .

What is the function of delete operator ?

The functionality of delete operator is used to delete all variables and objects in a program but it cannot delete variables declared with VAR keyword.