JavaScript Interview Questions with Answers Page II

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1. Methods GET and POST in HTML forms - what's the difference?.

GET: Parameters are passed in the querystring. Maximum amount of data that can be sent via the GET method is limited to about 2kb.

POST: Parameters are passed in the request body. There is no limit to the amount of data that can be transferred using POST. However, there are limits on

the maximum amount of data that can be transferred in one name/value pair.

2. How to write a script for "Select" lists using javascript

1. To remove an item from a list set it to null

mySelectObject.options[3] = null;

2. To truncate a list set its length to the maximum size you desire

mySelectObject.length = 2;

3. To delete all options in a select object set the length to 0.

mySelectObject.leng

3. Text From Your Clipboard?

It is true, text you last copied for pasting (copy & paste) can be stolen when you visit web sites using a combination of JavaScript and ASP (or PHP, or

CGI) to write your possible sensitive data to a database on another server.

4. What does the "Access is Denied" IE error mean?

The "Access Denied" error in any browser is due to the following reason.

A javascript in one window or frame is tries to access another window or frame whose

document's domain is different from the document containing the script.

5. Is a javascript script faster than an ASP script?

Yes.Since javascript is a client-side script it does require the web server's help for its

computation,so it is always faster than any server-side script like ASP,PHP,etc..

6. Are Java and JavaScript the Same?

No.java and javascript are two different languages.

Java is a powerful object - oriented programming language like C++,C whereas Javascript is a

client-side scripting language with some limitations.

7. How to embed javascript in a web page?

javascript code can be embedded in a web page between <script

language="javascript"></script> tags

8. What and where are the best JavaScript resources on the Web?

The Web has several FAQ areas on JavaScript. The best place to start is something called the meta-FAQ [14-Jan-2001 Editor's Note: I can't point to it

anymore, it is broken!], which provides a high-level overview of the JavaScript help available on the Net. As for fact-filled FAQs, I recommend one

maintained by Martin Webb and a mini-FAQ that I maintain.

For interactive help with specific problems, nothing beats the primary JavaScript Usenet newsgroup, comp.lang.javascript. Depending on my work backlog, I

answer questions posted there from time to time. Netscape and Microsoft also have vendor-specific developer discussion groups as well as detailed

documentation for the scripting and object model implementations.

9. What are the problems associated with using JavaScript, and are there JavaScript techniques that you discourage?

Browser version incompatibility is the biggest problem. It requires knowing how each scriptable browser version implements its object model. You see, the

incompatibility rarely has to do with the core JavaScript language (although there have been improvements to the language over time); the bulk of

incompatibility issues have to do with the object models that each browser version implements. For example, scripters who started out with Navigator 3

implemented the image rollover because it looked cool. But they were dismayed to find out that the image object wasn't scriptable in Internet Explorer 3

or Navigator 2. While there are easy workarounds to make this feature work on newer browsers without disturbing older ones, it was a painful learning

experience for many.

The second biggest can of worms is scripting connections between multiple windows. A lot of scripters like to have little windows pop up with navigation

bars or some such gizmos. But the object models, especially in the older browser versions, don't make it easy to work with these windows the minute you

put a user in front of them--users who can manually close windows or change their stacking order. More recently, a glitch in some uninstall routines for

Windows 95 applications can disturb vital parts of the system Registry that Internet Explorer 4 requires for managing multiple windows. A scripter can't

work around this problem, because it's not possible to detect the problem in a user's machine. I tend to avoid multiple windows that interact with each

other. I think a lot of inexperienced Web surfers can also get confused by them.

10. What boolean operators does JavaScript support?

&&, || and !

11. What does "1"+2+4 evaluate to?

Since 1 is a string, everything is a string, so the result is 124.

12. What are the ways to emit client-side JavaScript from server-side code in ASP.NET?

The Page object in ASP.NET has two methods that allow emitting of client-side JavaScript:

RegisterClientScriptBlock and RegisterStartupScript.

Example usage:

Page.RegisterClientScriptBlock("ScriptKey", "<script language=javascript>" + "function TestFn() { alert('Clients-side JavaScript'); }</script>");

Page.RegisterStartupScript("ScriptKey", "<script language=javascript>" + "function TestFn() { alert('Clients-side JavaScript'); }</script>");

ScriptKey is used to suppress the same JavaScript from being emitted more than once. Multiple calls to RegisterClientScriptBlock or RegisterStartupScript

with the same value of ScriptKey emit the script only once, on the first call.

13. What is the difference between RegisterClientScriptBlock and RegisterStartupScript?

RegisterClientScriptBlock emits the JavaScript just after the opening

tag. RegisterStartupScript emits the JavaScript at the bottom of the ASP.NET page just before the closing tag.

14. What is the difference between a web-garden and a web-farm?

Web-garden - An IIS6.0 feature where you can configure an application pool as a web-garden and also specify the number of worker processes for that pool.

It can help improve performance in some cases.

Web-farm - a general term referring to a cluster of physically separate machines, each running a web-server for scalability and performance (contrast

this with web-garden which refers to multiple processes on one single physical machine).

15. How to get the contents of an input box using Javascript?

Use the "value" property.

var myValue = window.document.getElementById("MyTextBox").value;

16. How to determine the state of a checkbox using Javascript?

var checkedP = window.document.getElementById("myCheckBox").checked;

17. How to set the focus in an element using Javascript?

<script> function setFocus() { if(focusElement != null) { document.forms[0].elements["myelementname"].focus(); } } </script>

18. How to access an external javascript file that is stored externally and not embedded?

This can be achieved by using the following tag between head tags or between body tags.

<script src="abc.js"></script>How to access an external javascript file that is stored externally and not embedded? where abc.js is the external

javscript file to be accessed.

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

An alert box displays only one button which is the OK button whereas the Confirm box

displays two buttons namely OK and cancel.

20. What is a prompt box?

A prompt box allows the user to enter input by providing a text box.

21. Can javascript code be broken in different lines?

Breaking is possible within a string statement by using a backslash \ at the end but not within any other javascript statement.

that is ,

document.write("Hello \ world");

is possible but not document.write \

("hello world");

22. Taking a developer’s perspective, do you think that that JavaScript is easy to learn and use?

One of the reasons JavaScript has the word "script" in it is that as a programming language, the vocabulary of the core language is compact compared to

full-fledged programming languages. If you already program in Java or C, you actually have to unlearn some concepts that had been beaten into you. For

example, JavaScript is a loosely typed language, which means that a variable doesn't care if it's holding a string, a number, or a reference to an

object; the same variable can even change what type of data it holds while a script runs.

The other part of JavaScript implementation in browsers that makes it easier to learn is that most of the objects you script are pre-defined for the

author, and they largely represent physical things you can see on a page: a text box, an image, and so on. It's easier to say, "OK, these are the things

I'm working with and I'll use scripting to make them do such and such," instead of having to dream up the user interface, conceive of and code objects,

and handle the interaction between objects and users. With scripting, you tend to write a _lot_ less code.

23. What Web sites do you feel use JavaScript most effectively (i.e., best-in-class examples)? The worst?

The best sites are the ones that use JavaScript so transparently, that I'm not aware that there is any scripting on the page. The worst sites are those

that try to impress me with how much scripting is on the page.

24. How about 2+5+"8"?

Since 2 and 5 are integers, this is number arithmetic, since 8 is a string, it’s concatenation, so 78 is the result.

25. What is the difference between SessionState and ViewState?

ViewState is specific to a page in a session. Session state refers to user specific data that can be accessed across all pages in the web application.

26. unescape(), escape()

These are similar to the decodeURI() and encodeURI(), but escape() is used for only portions of a URI.

<script type="text/javascript">

var myvalue = "Sir Walter Scott";

document.write("Original myvalue: "+myvalue);

document.write("
escaped: "+escape(myvalue));

document.write("
uri part: \"&author="+escape(myvalue)+"\"");

</script>

If you use escape() for the whole URI... well bad things happen.

<script type="text/javascript">

var uri = "http://www.google.com/search?q=sonofusion Taleyarkhan"

document.write("Original uri: "+uri);

document.write("

escaped: "+escape(uri));

v/script>

27. decodeURI(), encodeURI()

Many characters cannot be sent in a URL, but must be converted to their hex encoding. These functions are used to convert an entire URI (a superset of

URL) to and from a format that can be sent via a URI.

<script type="text/javascript">

var uri = "http://www.google.com/search?q=sonofusion Taleyarkhan"

document.write("Original uri: "+uri);

document.write("
encoded: "+encodeURI(uri));

</script>