Question 1

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

Accepted Answer

An alert box displays only one button which is the OK button whereas the Confirm box displays two buttons namely OK and cancel

Question 2

How do you create a new object in JavaScript?

Accepted Answer

var obj = new Object(); or var obj = {};

Question 3

Does javascript have the concept level scope?

Accepted Answer

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 4

Are javascript and jQuery different?

Accepted Answer

jQuery is a quick as well as concise JavaScript Library that simplifies HTML document traversing, animating, event handling, & Ajax interactions for the purpose of quick web development needs So although they are not entirely different, both are not the same either!

Question 5

How JavaScript timers work? What is a drawback of JavaScript timers?

Accepted Answer

Timers allow you to execute code at a set time or repeatedly using an interval This is accomplished with the setTimeout, setInterval, and clearInterval functions The setTimeout(function, delay) function initiates a timer that calls a specific function after the delay; it returns an id value that can be used to access it later The setInterval(function, delay) function is similar to the setTimeout function except that it executes repeatedly on the delay and only stops when cancelled The clearInterval(id) function is used to stop a timer Timers can be tricky to use since they operate within a single thread, thus events queue up waiting to execute

Question 6

What is Javascript namespacing? How and where is it used?

Accepted Answer

Using global variables in Javascript is evil and a bad practice That being said, namespacing is used to bundle up all your functionality using a unique name In JavaScript, a namespace is really just an object that you’ve attached all further methods, properties and objects It promotes modularity and code reuse in the application

Question 7

What are the different objects used in JavaScripts?

Accepted Answer

JavaScripts uses a hierarchical structure that applies to the objects in a document There are some objects that show the relationship of one object to another using the language Window object: This is the topmost object in the hierarchy It represent the content area of browser window that consists of HTML documents Each frame is also a window that has some actions inside it Document object: This object gets loaded in a window and consists of objects of different kind in the model It consists of the content that will be written in the script Form object: Form objects are used for more interaction with the users It represents the form elements inside tag

Question 8

What does window.history object?

Accepted Answer

The windowhistory object can be written without the window prefix To protect the privacy of the users, there are limitations to how JavaScript can access this object Some methods: historyback() - same as clicking back in the browser historyforward() - same as clicking forward in the browser

Question 9

Which of the following is added to prefs.js,when open a dialog box each time an error occurs?

Accepted Answer

user_pref("javascript.classic.error_alerts", true);

Question 10

Which of the following navigator object properties is the same in both Netscape and IE?

Accepted Answer

navigator.appCodeName

Question 11

What is mean by "this" keyword in javascript?

Accepted Answer

It refers current object

Question 12

What does isNaN function do?

Accepted Answer

It Return true if the argument is not a number

Question 13

What is the difference between "==" and "==="?

Accepted Answer

"==" checks equality only, "===" checks for equality as well as the type

Question 14

What are the new features provided in HTML5?

Accepted Answer

Some of the new features provided in HTML5 are: - It provides support for local storage - New form controls, like calendar, date, time, email, url, search - element is provided to facilitate 2D drawing - The and elements are provided for media playback - New content-specific elements are provided For eg , , , ,

Question 15

Differentiate between Canvas and SVG.

Accepted Answer

Some important differences between Canvas and SVG: - Canvas is resolution dependent while SVG is not - Canvas does not provide any support for event handlers while SVG does - Canvas is suitable for graphic-intensive games while SVG is not suitable for gaming - Canvas is suitable for small rendering areas while SVG is suitable for large rendering areas like Google maps

Question 16

What is SVG?

Accepted Answer

- SVG is the abbreviation for Scalable Vector Graphics and is recommended by W3C - It is used to define vector-based graphics for the Web - The graphics are defined in XML format -An important quality of SVG graphics is that their quality is maintained even when they are zoomed or resized - All the element and attributes of SVG files can be animated

Question 17

What is a Canvas?

Accepted Answer

Canvas is a rectangular area on a HTML page, specified with the tag

Question 18

What is HTML5 Web Storage?

Accepted Answer

With HTML5, it is possible for the web pages to store the data locally in the user's browser This web storage is much faster and secured than the cookies Also, a larger amount of data can be stored without causing any adverse effect to the performance of the website The data here is not included with every server request It is used ONLY when it is asked for It is only that particular web page that can access the data stored by itself

Question 19

Differentiate between localStorage and sessionStorage objects.

Accepted Answer

- localStorage object stores the data without an expiry date while sessionStorage object stores the data only for one session - With localStorage object, data will not be deleted when the browser window is closed while the data is deleted when the browser window closes with sessionStorage objects

Question 20

What is the concept of Application Cache in HTML5? What are its advantages?

Accepted Answer

The Application Cache concept introduced by HTML5 means that a web application is cached, and accessible without an internet connection There are three advantages of Application Cache: 1Offline browsing - users can use the application when they're offline 2Speed - cached resources load faster 3Reduced server load - the browser will only download updated/changed resources from the server

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