JavaScript

Question 1

What is JavaScript?

Answer 1

JavaScript is a client-side as well as server side scripting language that can be inserted into HTML pages and is understood by web browsers. JavaScript is also an Object based Programming language

Question 2

What are JavaScript Data Types?

Answer 2

Following are the JavaScript Data types:

Number
String
Boolean
Object
Undefined

Question 3

What is the use of isNaN function?

Answer 3

isNan function returns true if the argument is not a number otherwise it is false.

Question 4

Which company developed JavaScript?

Answer 4

Netscape is the software company who developed JavaScript.

Question 5

What are undeclared and undefined variables?

Answer 5

Undeclared variables are those that do not exist in a program and are not declared. If the program tries to read the value of an undeclared variable, then a runtime error is encountered.

Undefined variables are those that are declared in the program but have not been given any value. If the program tries to read the value of an undefined variable, an undefined value is returned.

Question 6

What is ‘this’ keyword in JavaScript?

Answer 6

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

Question 7

What are all the looping structures in JavaScript?

Answer 7

Following are looping structures in Javascript:

For
While
do-while loops

Question 8

How can you convert the string of any base to integer in JavaScript?

Answer 8

The parseInt() function is used to convert numbers between different bases. parseInt() takes the string to be converted as its first parameter, and the second parameter is the base of the given string.

Question 9

Explain the difference between the double equals operator(“==”) and the triple equals operator (“===”)?

Answer 9

”==” checks only for equality in value whereas “===” is a stricter equality test and returns false if either the value or the type of the two variables are different.

Question 10

What do mean by NULL in Javascript?

Answer 10

The NULL value is used to represent no value or no object. It implies no object or null string, no valid boolean value, no number and no array object.

Question 11

What is an undefined value in JavaScript?

Answer 11

Undefined value means the

Variable used in the code doesn’t exist
Variable is not assigned to any value
Property doesn’t exist

Question 12

What is the difference between an alert box and a confirmation box?

Answer 12

An alert box displays only one button which is the OK button.

But a Confirmation box displays two buttons namely OK and cancel.

Question 13

What are JavaScript Cookies?

Answer 13

Cookies are the small test files stored in a computer and it gets created when the user visits the websites to store information that they need. Example could be User Name details and shopping cart information from the previous visits.

Question 14

Which keyword is used to print the text in the screen?

Answer 14

document.write(“Welcome”) is used to print the text – Welcome in the screen.

Question 15

What is the use of Push method in JavaScript?

Answer 15

The push method is used to add or append one or more elements to the end of an Array. Using this method, we can append multiple elements by passing multiple arguments

Question 16

What boolean operators can be used in JavaScript?

Answer 16

The ‘And’ Operator (&&), ‘Or’ Operator (||) and the ‘Not’ Operator (!) can be used in JavaScript.

Question 17

What is an AJAX call?

Answer 17

AJAX stands for Asynchronous JavaScript And XML. In a nutshell, it is the use of the XMLHttpRequest object to communicate with servers. It can send and receive information in various formats, including JSON, XML, HTML, and text files.

Question 18

What are synchronous and asynchronous calls?

Answer 18

Synchronous: If an API call is synchronous, it means that code execution will block (or wait) for the API call to return before continuing. … Asynchronous calls do not block (or wait) for the API call to return from the server.

Question 19

Is an AJAX call asynchronous?

Answer 19

Yes. AJAX stands for asynchronous JavaScript and XML,

Question 20

what is a promise in JavaScript?

Answer 20

A promise is an object that may produce a single value some time in the future : either a resolved value, or a reason that it’s not resolved (e.g., a network error occurred). A promise may be in one of 3 possible states: fulfilled, rejected, or pending.

Question 21

What protocol is REST built around?

Answer 21

REST uses the HTTP Protocol.

Question 22

What are “Normal Forms” in databasing?

Answer 22

Normal forms are used to eliminate or reduce redundancy in database tables.

Question 23

What does REST stand for?

Answer 23

REST stands for Representational State Transfer.

Question 24

How can you tell what browser is being used in JS?

Answer 24

JavaScript has a standard object called navigator that contains data about the browser being used.

Question 25

What is a Polyfill?

Answer 25

A polyfill is a piece of code used to provide modern functionality on older browsers that do not natively support it. … The polyfill uses non-standard features in a certain browser to give JavaScript a standards-compliant way to access the feature.

Question 26

What is the difference between “var” and “let”?

Answer 26

Let uses block scope, while Var uses hoisting when loading.

Question 27

What are the data types in JavaScript?

Answer 27

Boolean, String, Number, Null, Undefined, BigInt, Symbol, and Object.

Question 28

How are JavaScript Numbers stored?

Answer 28

JavaScript numbers are always stored as double precision floating point numbers, following the international IEEE 754 standard.