Java Script Interview Questions and Answers

What is JavaScript?
JavaScript is a scripting language, designed to add interactivity to HTML pages, JavaScript is usually embedded directly into HTML pages, and JavaScript is an interpreted language (means that scripts execute without preliminary compilation) JavaScript is a platform-independent, event-driven, interpreted client-side scripting and programming language developed by Netscape Communications Corp. and Sun Microsystems.
Define JavaScript Variables?

JavaScript is case-sensitive, variable names are case-sensitive. Creating variables in JavaScript is most often referred to as "declaring" variables. You declare JavaScript variables with the var keyword:
Var x;
Var fu='hi';
Var gf=3.45;

What is variable typing in java script?
It is perfectly legal to assign a number to a variable and then assign a string to the same variable as follows example i = 10; i = 'stringchar'; This is called variable typing
How do you create an object in JavaScript?
var person = new Object; or var person = {};
Are Java and JavaScript the same?
NO! Java and JavaScript are two completely different languages in both concept and design! Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++. JavaScript’s syntax is loosely based on Java
What's relationship between JavaScript and ECMA Script?

ECMA Script is yet another name for JavaScript (other names include Live Script). The current JavaScript that you see supported in browsers is ECMA Script revision 3. Java Script is a scripting language that has been widely accepted for client side web development. However it originated from ECMA standards. ECMA and live scripts are just other names of java script.

What Boolean operators does JavaScript support?
&&, || ,!
What looping structures are there in JavaScript?
For, while, do-while loops
What is the difference between undefined value and null value?
Undefined means a variable has been declared but has not yet been assigned a value. On the other hand, null is an assignment value. It can be assigned to a variable as a representation of no value. Also, undefined and null are two distinct types: undefined is a type itself (undefined) while null is an object. Unassigned variables are initialized by JavaScript with a default value of undefined. JavaScript never sets a value to null. That must be done programmatically.

What data types are supported in Java Script?
Number, String, Undefined, null, Boolean
Explain a JavaScript Comments?

Comments can be added to explain the JavaScript, or to make the code more readable.
Single line comments start with //.
Multi line comments start with /* and end with */

What does the tag do?
Displayed the text enclosed within tag when JavaScript is disabled
What is === operator in JavaScript and how it is different from == operator?

=== operator checks for the equality. It gives true when both the compared values are having same value and same data type as === does not perform any type conversion while comparing. 

It is different from == as == does the type conversion while comparing.

What is the difference between JavaScript and Jscript?

Jscript supports more rich set of functionality/commands than the java script, through which ActiveX and local computer can be accessed. These commands are used in an intranet where the connecting computer's configuration is known and they are all being accessed using Internet Explorer. While java script targets unknown machine configuration and Jscript cannot for which java script are suitable for internet which Jscripts are not.

What is the main difference between Client side JavaScript and Server side Java Script? How actually they run on both side?

To state the main difference, JavaScript at the client side does not require a web server to make it run instead it uses the client's processor for this purpose. This eradicates the portability issue. But in server side JavaScript deployment, portability, configuration are major and vast issues and requires a web server to run the script within a page before rendering its output as a response html page.

How can JavaScript make a Web site easier to use?
JavaScript’s run on the client side which saves the server roundtrip time for small processing. It means that it makes web pages more interactive as everything is not required to be submitted at the server. Let’s consider a small clock if controlled by the server then the transmission time will make the clock faulty in this case java script is used.

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Simplification

By what number should we multiply -1/5 so that the product may be 9/25?

Profit and Loss

A person sells an article for Rs 550, gaining 1/10 of its cost price. Its gain percentage is.

Algebra

If 3x + 2y = 12 and xy = 6, then 9x2 + 4y2 = ______.

Volume and Surface Area

In a temple there are 25 cylindrical pillars. The radius of each pillar is 28cm and height 4m. The total cost of painting the curved surface area of pillars at the rate of Rs. 8 per m2 is:

Problems on Ages

After 12 years, I shall be 3 times as old as I was 4 years ago. My present age is:

Square and Cube Root

The smallest number by which 1100 must be multiplied so that the product becomes a perfect square is____.

Probability

What is the probability that a number selected from the numbers 1, 2, 3,…….,25 is a prime number, when each of the given numbers is equally likely to be selected?

Square and Cube Root

What is the smallest number by which 3087 must be divided so that the quotient is a perfect cube?

Physics

The most comfortable distance at which one can read with a normal eye is:

Biology

Cholera is caused by:

Write the name of reptile with four chambered heart?

Compound Interest

Raj borrowed Rs. 5000 at 10% per annum on simple interest and lent the same amount at 15% per annum on compound interest. At the end of 2 years, he would ?

Area

If the area of a square is 16 cm2, then the area of the square joining the mid-points of the sides is?

General Knowledge of MP

Vidisha is situated on the banks of river?

General Knowledge of World

When is the Human Rights Day celebrated?

Profit and Loss

By selling coconuts at the rate of Rs. 6/- each, a trader gained 20%. Find the cost of 100 coconuts?

General Knowledge of India

How many coastal state are in India?

Numbers

A person is to count 4500 currency notes. Let an denote the number of notes he counts in the nth minute. If a1 = a2 = .... = a10 = 150 and a10 , a11 ,... are in an AP with common difference – 2, then the time taken by him to count all notes is ?