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.

Latest Updates

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 ?

The value of product 6 1/2 * 6 1/4 * 6 1/8 * 6 1/16 * -----∞ upto infinite terms?

Unix/Linux

What is nohup command in unix?

How do display the 10th, 11th and 12th line of a file in Unix?

Average

The mean of 100 students marks was found to be 40. it was found later that a mark 53 was read as 83. the correct mean is?

Numbers

The geometric mean of three observations 40, 50 and X is 10, then the value of X is ?

Indian Politics

Who appoints the members of National human rights commission?

The President of India can resign by writing under his hand addressed to?

Under which article of the constitution of India can the President of India refer a matter to the Supreme Court for its opinion?

General Computer Knowledge

The term VPN stands for ?

The transmission control protocol(TCP) is a............ layer protocol ?

Oracle PL/SQL

What is the difference between Procedure and Function?

Define exception and How will you raise an exception in PL/SQL procedure?

What is the advantage of using packages for storing PL/SQL objects?

Fill in the blank

I ________ station before the train arrived.

If I ______ a king, I would help everyone.

Radha___________her daughter for an hour.

Errors Identification

Find out which part of the sentence below has an error and mark the option accourdingly -
Sohan was married in 1990 and have three children.