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Java Script Interview Questions Answers

Question 1 : Are Java and JavaScript the Same?

Answer 1 : 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.

Question 2 : Are you concerned that older browsers don't support JavaScript and thus exclude a set of Web users? individual users?

Answer 2 : 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. The situation makes scripting a challenge, especially for newcomers who may not be aware of the limitations of earlier browsers. A lot of effort in my books and ancillary material goes toward helping scripters know what features work in which browsers and how to either workaround limitations in earlier browsers or raise the compatibility common denominator. 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.

Question 3 : Can javascript code be broken in different lines?

Answer 3 : 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");

Question 4 : decodeURI(), encodeURI()

Answer 4 : 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("<br />encoded: "+encodeURI(uri)); </script>

Question 5 : Does javascript have the concept level scope?

Answer 5 : 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.

Question 6 : eval()?

Answer 6 : The eval() method is incredibly powerful allowing you to execute snippets of code during execution. <script type="text/javascript"> var USA_Texas_Austin = "521,289"; document.write("Population is "+eval("USA_"+"Texas_"+"Austin")); </script> This produces Population is 521,289

Question 7 : How about 2+5+"8"?

Answer 7 : Since 2 and 5 are integers, this is number arithmetic, since 8 is a string, it’s concatenation, so 78 is the result.

Question 8 : How can JavaScript be used to improve the "look and feel" of a Web site? By the same token, how can JavaScript be used to improve the user interface?

Answer 8 : On their own, Web pages tend to be lifeless and flat unless you add animated images or more bandwidth-intensive content such as Java applets or other content requiring plug-ins to operate (ShockWave and Flash, for example). Embedding JavaScript into an HTML page can bring the page to life in any number of ways. Perhaps the most visible features built into pages recently with the help of JavaScript are the so-called image rollovers: roll the cursor atop a graphic image and its appearance changes to a highlighted version as a feedback mechanism to let you know precisely what you're about to click on. But there are less visible yet more powerful enhancements to pages that JavaScript offers. Interactive forms validation is an extremely useful application of JavaScript. While a user is entering data into form fields, scripts can examine the validity of the data--did the user type any letters into a phone number field?, for instance. Without scripting, the user has to submit the form and let a server program (CGI) check the field entry and then report back to the user. This is usually done in a batch mode (the entire form at once), and the extra transactions take a lot of time and server processing power. Interactive validation scripts can check each form field immediately after the user has entered the data, while the information is fresh in the mind. Another helpful example is embedding small data collections into a document that scripts can look up without having to do all the server programming for database access. For instance, a small company could put its entire employee directory on a page that has its own search facility built into the script. You can cram a lot of text data into scripts no larger than an average image file, so it's not like the user has to wait forever for the data to be downloaded. Other examples abound, such as interactive tree-structure tables of contents. More modern scriptable browsers can be scripted to pre-cache images during the page's initial download to make them appear lickety-split when needed for image swapping. I've even written some multi-screen interactive applications that run entirely on the client, and never talk to the server once everything is downloaded.

Question 9 : How can JavaScript be used to personalize or tailor a Web site to fit individual users?

Answer 9 : JavaScript allows a Web page to perform "if-then" kinds of decisions based on browser version, operating system, user input, and, in more recent browsers, details about the screen size in which the browser is running. While a server CGI program can make some of those same kinds of decisions, not everyone has access to or the expertise to create CGI programs. For example, an experienced CGI programmer can examine information about the browser whenever a request for a page is made; thus a server so equipped might serve up one page for Navigator users and a different page for Internet Explorer users. Beyond browser and operating system version, a CGI program can't know more about the environment. But a JavaScript-enhanced page can instruct the browser to render only certain content based on the browser, operating system, and even the screen size. Scripting can even go further if the page author desires. For example, the author may include a preference screen that lets the user determine the desired background and text color combination. A script can save this information on the client in a well-regulated local file called a cookie. The next time the user comes to the site, scripts in its pages look to the cookie info and render the page in the color combination selected previously. The server is none the wiser, nor does it have to store any visitor-specific information.

Question 10 : 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?

Answer 10 : 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.

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