What is JavaScript?
JavaScript is a platform-independent,event-driven, interpreted client-side scripting and programming language developed by Netscape Communications Corp. and Sun Microsystems.
How is JavaScript different from Java?
JavaScript was developed by Brendan Eich of Netscape; Java was developed at Sun Microsystems. While the two languages share some common syntax, they were developed independently of each other and for different audiences. Java is a full-fledged programming language tailored for network computing; it includes hundreds of its own objects, including objects for creating user interfaces that appear in Java applets (in Web browsers) or standalone Java applications. In contrast, JavaScript relies on whatever environment it's operating in for the user interface, such as a Web document's form elements.
What’s relationship between JavaScript and ECMAScript?
ECMAScript is yet another name for JavaScript (other names include LiveScript). The current JavaScript that you see supported in browsers is ECMAScript revision 3.
How do you submit a form using Javascript?
Use document.forms[0].submit();
(0 refers to the index of the form – if you have more than one form in a page, then the first one has the index 0, second has index 1 and so on).
How to read and write a file using javascript?
I/O operations like reading or writing a file is not possible with client-side javascript. However , this can be done by coding a Java applet that reads files for the script.
How to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.appVersion
string (property) should be used.
How can JavaScript make a Web site easier to use? That is, are there certain JavaScript techniques that make it easier for people to use a Web site?
JavaScript's greatest potential gift to a Web site is that scripts can make the page more immediately interactive, that is, interactive without having to submit every little thing to the server for a server program to re-render the page and send it back to the client. For example, consider a top-level navigation panel that has, say, six primary image map links into subsections of the Web site. With only a little bit of scripting, each map area can be instructed to pop up a more detailed list of links to the contents within a subsection whenever the user rolls the cursor atop a map area. With the help of that popup list of links, the user with a scriptable browser can bypass one intermediate menu page. The user without a scriptable browser (or who has disabled JavaScript) will have to drill down through a more traditional and time-consuming path to the desired content.
What are JavaScript types?
Number, String, Boolean, Function, Object, Null, Undefined.
How do you convert numbers between different bases in JavaScript?
Use the parseInt() function, that takes a string as the first parameter, and the base as a second parameter. So to convert hexadecimal 3F to decimal, use parseInt ("3F", 16);
How to create arrays in JavaScript?
We can declare an array like this
var scripts = new Array();
We can add elements to this array like this
scripts[0] = "PHP";
scripts[1] = "ASP";
scripts[2] = "JavaScript";
scripts[3] = "HTML";
Now our array scrips has 4 elements inside it and we can print or access them by using their index number. Note that index number starts from 0. To get the third element of the array we have to use the index number 2 . Here is the way to get the third element of an array.
document.write(scripts[2]);
We also can create an array like this
var no_array = new Array(21, 22, 23, 24, 25);
What is a fixed-width table and its advantages?
Fixed width tables are rendered by the browser based on the widths of the columns in the first row, resulting in a faster display in case of large tables. Use the CSS style table-layout:fixed to specify a fixed width table.
If the table is not specified to be of fixed width, the browser has to wait till all data is downloaded and then infer the best width for each of the columns.
Where are cookies actually stored on the hard disk?
This depends on the user's browser and OS.
In the case of Netscape with Windows OS,all the cookies are stored in a single file called
What can javascript programs do?
Generation of HTML pages on-the-fly without accessing the Web server. The user can be given control over the browser like User input validation Simple computations can be performed on the client's machine The user's browser, OS, screen size, etc. can be detected Date and Time Handling
How to set a HTML document's background color?
document.bgcolor property can be set to any appropriate color.
Are you concerned that older browsers don't support JavaScript and thus exclude a set of Web users? individual users?
Fragmentation of the installed base of browsers will only get worse. By definition, it can never improve unless absolutely everyone on the planet threw away their old browsers and upgraded to the latest gee-whiz versions. But even then, there are plenty of discrepancies between the scriptability of the latest Netscape Navigator and Microsoft Internet Explorer.
Designing scripts for a Web site requires making some hard decisions about if, when, and how to implement the advantages scripting offers a page to your audience. For public Web sites, I recommend using scripting in an additive way: let sufficient content stand on its own, but let scriptable browser users receive an enhanced experience, preferably with the same HTML document.
What does isNaN function do?
Return true if the argument is not a number.
What is negative infinity?
It’s a number in JavaScript, derived by dividing negative number by zero.
In a pop-up browser window, how do you refer to the main browser window that opened it?
Use window.opener to refer to the main window from pop-ups.
What is the data type of variables of in JavaScript?
All variables are of object type in JavaScript.
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
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.
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.
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..
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.
How to embed javascript in a web page?
javascript code can be embedded in a web page between
tags
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.
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.
What Boolean operators does JavaScript support?
&&, and !
What does "1"+2+4 evaluate to?
Since 1 is a string, everything is a string, so the result is 124.
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).
How to get the contents of an input box using Javascript?
Use the "value" property.
var myValue = window.document.getElementById("MyTextBox").value;
How to determine the state of a checkbox using Javascript?
var checkedP = window.document.getElementById("myCheckBox").checked;
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.
What is a prompt box?
A prompt box allows the user to enter input by providing a text box.
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");
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.
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.
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.
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.
What does the EnableViewStateMac setting in an aspx page do?
Setting EnableViewStateMac=true is a security measure that allows ASP.NET to ensure that the viewstate for a page has not been tampered with. If on Postback, the ASP.NET framework detects that there has been a change in the value of viewstate that was sent to the browser, it raises an error - Validation of viewstate MAC failed.
Use <%@ Page EnableViewStateMac="true"%>to set it to true (the default value, if this attribute is not specified is also true) in an aspx page.
What looping structures are there in JavaScript?
for, while, do-while loops, but no foreach.
What does undefined value mean in javascript?
Undefined value means the variable used in the code doesn't exist or is not assigned any value or the property doesn't exist.
What is the difference between undefined value and null value?
(i)Undefined value cannot be explicitly stated that is there is no keyword called undefined whereas null value has keyword called null
(ii)typeof undefined variable or property returns undefined whereas typeof null value returns object
What is variable typing in javascript?
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 = "string";
This is called variable typing
Does javascript have the concept level scope?
No. JavaScript does not have block level scope, all the variables declared inside a function possess the same level of scope unlike c,c++,java.
What are undefined and undeclared variables?
Undeclared variables are those that are not declared in the program (do not exist at all),trying to read their values gives runtime error.But if undeclared variables are assigned then implicit declaration is done .
Undefined variables are those that are not assigned any value but are declared in the program.Trying to read such variables gives special value called undefined value.
What is === operator ?
==== is strict equality operator ,it returns true only when the two operands are having the same value without any type conversion.
How to disable an HTML object ?
document.getElementById("myObject").disabled = true;
How to make elements invisible ?
Change the "visibility" attribute of the style object associated with your element. Remember that a hidden element still takes up space, use "display" to make the space disappear as well.
if ( x == y) {
myElement.style.visibility = 'visible';
} else {
myElement.style.visibility = 'hidden';
}
How to set the cursor to wait ?
In theory, we should cache the current state of the cursor and then put it back to its original state.
document.body.style.cursor = 'wait';
//do something interesting and time consuming
document.body.style.cursor = 'auto';
How to reload the current page ?
window.location.reload(true);
