Javascript Interview Question and Answers

Javascript Interview Question and Answers
1.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.
2.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.
3.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.
4.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
5.How to set a HTML document's background color?
document.bgcolor property can be set to any appropriate color.
6.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.
7.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..
8.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.
9.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.
10.What is a prompt box?
A prompt box allows the user to enter input by providing a text box.
11.What does javascript null mean?
Ans.The null value is a unique value representing no value or no object.
It implies no object,or null string,no valid boolean value,no number and no array object.
12.What does undefined value mean in javascript?
Ans.Undefined value means the variable used in the code doesnt exist or is not assigned any value or the property doesnt exist.
13.What is the difference between undefined value and null value?Ans.(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

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