jQuery is not a language but it is a well written code. jQuery is a set of JavaScript libraries that have been designed specifically to simplify HTML document traversing, animation, event handling, and Ajax interactions. jQuery is fast and lightweight. There are many other JavaScript code libraries such as MooTools, but jQuery has become the most popular because it is so easy to use.

We use jQuery due to following advantages:

• It is easy to use and learn.
• It helps to improve the performance of the application.
• It simplifies the task of creating highly responsive web pages.
• It helps to develop most browser compatible web page as it works across modern browsers.
• It helps to implement UI related critical functionality without writing hundreds of lines of codes.
• It abstracts away browser-specific features, allowing you to concentrate on design.
• It leverages your existing knowledge of CSS
• It performs multiple operations on a set of elements with one line of code (known as statement chaining)
• It is extensible so you can use third-party-plug-ins to perform specialized tasks or write your own.

JavaScript is a language while jQuery is a set of JavaScript libraries that have been designed specifically to simplify work like HTML document traversing, animation, event handling, and Ajax interactions.

No, jQuery is not a replacement of JavaScript. jQuery is a set of libraries which is written on top of JavaScript and have been designed specifically to simplify work.

jQuery is a library of JavaScript file.

jQuery is client side scripting.

No, if things can be done easily with css and javascript then you should not prefer jQuery because jQuery has some size and there is no point of wasting bandwidth.

Windows, Mac and Linux are more compatible with the jQuery.

First we need to download jQuery. jQuery comes in two versions:

• Development
• Production (which is compressed and minified)

jQuery file can be downloaded from jQuery Official website.

Typically, we download both versions and then use each one for its intended purpose.After downloading of jquery file, to start work on jquery, you need to add reference of that file in your webpage.

jQuery file should be added to the Master page and can use access from the content page directly without having any reference to it.

The jQuery library provides the jQuery function, which allows you to select elements using selectors.

var paragrapths = jQuery('p');

But generally when you see jQuery code then you will see that $ sign is used mostly:

var paragrapths = $('p');

$ sign in the code above is just a shorter and more convenient name for the jQuery function. Actually, in the jQuery source code, you'll find this code:

//Expose jQuery to the global object
window.jQuery = window.$ = jQuery;

Yes. We can use our own special character in place of $ sign. It is possible using jQuery.noConflict().

As we can use other client side libraries like MooTools, Prototype with jQuery and they also use $() as their global function and to define variables. This situation creates conflict as $() is used by jQuery and other library as their global function. To overcome from such situations, jQuery has introduced jQuery.noConflict().

jQuery.noConflict();
// Use jQuery via jQuery(...)
jQuery(document).ready(function(){
   jQuery("div").hide();
});  

You can also use your own specific character in the place of $ sign in jQuery.

var $j = jQuery.noConflict();
// Use jQuery via jQuery(...)
$j(document).ready(function(){
   $j("div").hide();
});  

Yes

.min.js is basically the minified version of jQuery file. Both the files are same as far as functionality is concerned. but .min.js is quite small in size so it loads quickly and saves bandwidth.

Minimized version is very small (approx 50% less) in size so it loads quickly, saves bandwidth and improve performance of website.

jQuery library comes in 2 different versions.

• Development
• Production/Deployment

As jQuery is open source, the development version is useful at development time and if you want to change something then you can make those changes in development version.

But the deployment version is minified version or compressed version so it is impossible to make changes in it. Because it is compressed, so its size is very less than the production version which affects the page load time.

There are 2 ways to debug jQuery:

• Add debugger; keyword to the line where you need to start debugging and then run Visual Studio in Debug mode with F5 function key.
• Insert a break point after attaching the process

.vsdoc file is used to provide intellisense support. We can even delete this file but if we will delete this file then we will loose the support of intellisense.

The starting point of jQuery code execution is $(document).ready() function which is executed when DOM is loaded.

Yes, We can have any number of document.ready() function on the same page.

These are the differences between onload() and document.ready():

• We can have as many document.ready() function in a page but we can have only single onload function in one body.
• document.ready() function is called as soon as DOM is loaded where body.onload() function is called when everything gets loaded on the page that includes DOM, images and all associated resources of the page.

jQuery.holdReady() function allows us to hold or delay execution of document.ready function. This function was introduced with release of jQuery 1.6. You need to pass value true or false in function as parameter to specify whether you want hold or resume.

$.holdReady(true);
$.getScript("someplugin.js", function() {
   $.holdReady(false);
});

CDN Stands for Content Distribution Network or also called Content Delivery Network is a group of computers placed at various points connected with network containing copies of data files to maximize bandwidth in accessing the data. In CDN, a client accesses a copy of data nearer to the client location rather than all clients accessing from the one particular server. This helps to achieve better performance of data retrieval by client.

• It reduces the load from your server.
• It saves bandwidth. jQuery framework will load faster from these CDN.
• It will be cached, if the user has visited any site which is using jQuery framework from any of these CDN

There are 3 popular jQuery CDNs.

• Google
• Microsoft
• jQuery

<script src="http://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.9/jquery-ui.js" type="text/javascript"></script>

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.9/jquery.min.js" type="text/javascript"></script>

<script type="text/javascript" src="http://code.jquery.com/jquery-1.9.1.min.js"></script>

It is a good approach to always use CDN but there may be a possibility (rare) that CDN is down. In that case you code will not work as jquery file will not be loaded. We can overcome this issue by following code:

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script type="text/javascript">
if (typeof jQuery == 'undefined') {
    document.write(unescape("%3Cscript src='Scripts/jquery.1.9.1.min.js' type='text/javascript'%3E%3C/script%3E"));
}
</script>

It first loads the jQuery from Google CDN and then check the jQuery object. If jQuery is not loaded successfully then it will references the jQuery.js file from hard drive location. In this example, the jQuery.js is loaded from Scripts folder.

Yes we can. See code below:

<script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>

Let's have an example. Your site is using HTTP protocol and you are moving from HTTP to HTTPS. Now you will have to make sure that correct protocol used for referencing jQuery library is HTTPS. "protocol-less" URL is the best way to reference third party content that’s available via both HTTP and HTTPS.

jQuery selectors retrieve content from the web page so that it can be manipulated using other functions. jQuery selectors return an array of objects that match the selection criteria.

jQuery filters operate on a selector to further refine the results array that the selector returns.

Yes we can use filters in jQuery without using of selectors.

There are many types of selectors. Please click here to know about each selectors.

We need to use # (hash) symbol to select element by ID selector in jQuery.

$("#test")

This selector selects element that has test as id attribute.

We need to use . (dot) symbol to select element by class name in jQuery.

$(".test")

This selector selects all the elements on which class test is applied.

You can use * (asterisk symbol) to select all page elements.

$("*").css("border","1px solid red");

The code will select all page elements and will apply border on them.

This will select all the div elements on page.

All the div element with parent class.

ID and element selectors are the fastest selectors in jQuery

class selectors are the slow compare to ID and element.

Selector execution is started from last. For Example:

$("div#test .abc");

jQuery will first find all the elements with class .abc and after that it will further refine selected elements by using first selector. It will reject all the other elements which are not in div#test.

As jQuery is written on top of JavaScript and it internally uses JavaScript only so JavaScript is always fast. In this scenario, jQuery method $('#txtFirstName') will internally makes a call to document.getElementByID('txtName').

this and $(this) both are same. When 'this' is wrapped in $() then it becomes a jQuery object and you can use the features of jQuery. The only difference is the way they are used.

$(document).ready(function(){
    $('#divTest').click(function(){
       alert($(this).text());
    });
});

In below example, this is an object but since it is not wrapped in $(), we can't use jQuery method so we have used the native JavaScript to get the text of div element.

$(document).ready(function(){
    $('#divTest').click(function(){
       alert(this.innerText);
    });
});

There are 2 ways to check an element if it is empty:

$(document).ready(function(){
   if ($('#div').is(':empty')){
      //div is empty
   }
}); 

$(document).ready(function(){
   if($.trim($('#div').html())==') {
      //div is empty
   }
}); 

eq() returns the element as a jQuery object that means that you can use jQuery functions on it.

get() return a DOM element. As it is a DOM element and it is not a jQuery-wrapped object So jQuery functions can't be used.

$('<div/>'): It creates a new div element. This is not added to DOM tree unless you don't append it to any DOM element.

$('div'): This is a selector and selects all the div elements of page.

The basic difference is the parent() function travels only one level in the DOM tree, where parents() function search through the whole DOM tree.

We can check existence of an element by using size() function or length property

$(document).ready(function(){
   if ($('#div').length > 0){
      //div exists
   }
});

$(document).ready(function(){
   if ($('#div').size()> 0){
      //div exists
   }
});

size() method and .length property both returns number of element in the object but the .length property is preferred to use because it does not have the overhead of a function call.

The $.each() function is used to iterate over any collection, whether it is an object or an array.

Both find() and children() methods are used to filter the child of the matched elements. But find() method is used to find all levels down the DOM tree but children() find single level down the DOM tree.

animate() function is used to create custom animation for many CSS properties on page element. It changes an element from one state to another with CSS styles. The CSS property value is changed gradually, to create an animated effect.

Only numeric values can be animated (like "margin:30px"). String values cannot be animated (like "background-color:red").

animate(params, duration, easing, callback)

• params: The css properties on the elements to animate
• duration: Specifies the speed of the animation. Default value is 400 milliseconds. Possible values: milliseconds, "slow“, "fast"
• easing: Specifies the speed of the element in different points of the animation. Default value is "swing". Possible values: "swing" - moves slower at the beginning/end, but faster in the middle "linear" - moves in a constant speed
• callback: The function to call when the animation is complete

$("btnClick").click(function(){
   $("#divTest").animate({height:"200px"});
});

"jQuery.fx.off" property is used to disable animation. If it is true then all animation methods will immediately set elements to their final state when called, rather than displaying an effect.

We can stop currently-running animation by using stop() method.

The .finish() method stops all queued animations and places the element(s) in their final state. This method was introduced in jQuery 1.9.

The .finish() method is similar to .stop(true, true) in that it clears the queue and the current animation jumps to its end value. It differs, however, in that .finish() also causes the CSS property of all queued animations to jump to their end values, as well.

These are some methods used to provide effects:

• show()
• hide()
• toggle()
• slideDown()
• slideUp()
• slideToggle
• fadeIn
• fadeOut
• fadeTo

All these methods are used to remove elements from DOM. But there are some differences between them.

.empty(): This method removes all the child elements of the matched elements.

.remove(): This method removes the element itself, as well as everything inside it. In addition to the elements themselves, all bound events and jQuery data associated with the elements are also removed.

.detach(): This method is the same as .remove(), except that .detach() keeps all jQuery data associated with the removed elements. This method is useful when removed elements are to be reinserted into the DOM at a later time.

attr() get the value of an attribute for the first matched element from the set of matched elements. prop() which was introduced in jQuery 1.6 gets the value of a property for the first matched element from the set of matched elements.

Attributes carry additional information about an HTML element and come in name="value" pairs. Where Property is a representation of an attribute in the HTML DOM tree. Once the browser parse your HTML code, corresponding DOM node will be created which is an object thus having properties.

attr() gives you the value of element as it was defines in the html on page load. It is always recommended to use prop() to get values of elements which is modified via javascript/jquery , as it gives you the original value of an element's current state.

jQuery.data() methods is used to associate the data with the DOM nodes and the objects. It store arbitrary data associated with the specified element and/or return the value that was set.

jQuery.data( document.body, "foo", 52 );

Yes, it is possible by .css which was provided in version 1.9:

var testVar= $("#divTest").css([ "width", "height", "backgroundColor" ]);
//now testVar variable will be and array like this:
{ 
   width: "100px", 
   height: "200px", 
   backgroundColor: "#FF00FF" 
}

Using "isNumeric()" function which was introduced with jQuery 1.7.

We can check data type of any variable by using $.type(Object) which returns the built-in JavaScript type for the object.

All these methods are used for attaching events to selectors or elements. But there are some differences between them.

.bind(): This is the easiest and quick method to bind events. bind() method only attach events to the current elements not future element. It will not bind events to elements added dynamically. It also has performance issues when dealing with a large selection.

.live(): This method overcomes the disadvantage of bind(). It works for dynamically added elements or future elements. But it also has performance issue on large pages. Chaining is also not properly supported using this method. Because of its poor performance, this method is deprecated as of jQuery 1.7 and you should stop using it.

.delegate(): The .delegate() method is same as .live() method, but instead of attaching the selector/event information to the document, you can choose where it is anchored. It also supports chaining.

.on(): Since live was deprecated with 1.7, so new method was introduced named ".on()". This method has all features provided by .bind(), .live() and .delegate().

We can use clone() method of jQuery to create clone of any object.

$(document).ready(function(){
   $('#btnClone').click(function(){
      $('#ddlCountry').clone().appendTo('body');
         return false;
   });
});

Default implementation of the clone() method doesn't copy events unless you tell the clone() method to copy the events. The clone() method takes a parameter, if you pass true then it will copy the events as well.

$(document).ready(function(){
   $('#btnClone').click(function(){
      $('#ddlCountry').clone(true).appendTo('body');
      return false;
   });
});

The event.preventDefault() method prevents the browser from executing the default action. For example, prevents a link from following the URL or prevents a submit button to submit the parent form.

The event.stopPropagation() method stops the bubbling of an event to parent elements. For example, if there is a link with a click event attached inside of a DIV or FORM that also has a click attached, it will prevent the DIV or FORM click event from firing.

event.preventDefault(): Prevents the browser from executing the default action.

event.stopPropagation(): Stops the bubbling of an event to parent elements

event.preventDefault() will prevent the default event from occurring, event.stopPropagation() will prevent the event from bubbling up and return false will do both.

event.stopPropagation() allows other handlers on the same element to be executed, while event.stopImmediatePropagation() prevents every event from running.

For example

$("div").click(function(e){
   e.stopImmediatePropagation();
});
$("div").click(function(e){
   // This function won't be executed
   $(this).css("background-color", "#f00");
});

If event.stopPropagation was used in previous example, then the next click event on div element which changes the css will fire, but in case event.stopImmediatePropagation(), the next div click event will not fire.

one() method of jQuery is used to attach a event to element which should be executed only once. The handler attached by method one() executes only once.

For Example:

$(document).ready(function() {
   $("#btnTest").one("click", function() {
      alert("This will be displayed only once.");
   });
});​

In this example message will be shown only once by clicking on btnTest button

Yes, jQuery can be used to make ajax request.

There are multiple ways to make ajax request in jQuery:

• load() : Load a piece of html into a container DOM
• $.getJSON(): Load JSON with GET method.
• $.getScript(): Load a JavaScript file.
• $.get(): Use to make a GET call and play extensively with the response.
• $.post(): Use to make a POST call and don't want to load the response to some container DOM.
• $.ajax(): Use this to do something on XHR failures, or to specify ajax options (e.g. cache: true) on the fly.

These are the four parameters for jQuery ajax method:

• url: Specifies Url to send request
• type: Specifies type of request (get or post)
• data: Specifies data to be sent to server
• cache: Whether the browser should cache the requested page or not

There is an advantage of using $ajax() for ajax call against $.get() or $.post(). $ajax() provide you more functionalities like error callback for handling error in response but $.get() and $.post() do not provide this functionality. You will have to always trust the response from server and believe that it is going to be successful all time in case of $.get() and $.post().

These objects help in handling asynchronous functions like Ajax.

Yes, We can execute/run multiple ajax request simultaneously in jQuery using .when() method which provides a way to execute callback functions based on one or more objects, usually Deferred objects that represent asynchronous events

Yes, We can call C# code-behind function via $.ajax. But for do that it is compulsory to mark the method as WebMethod.

ajaxError() function is used to handle ajax error globally in jQuery.

$( document ).ajaxError(function() {
   $( "span#log" ).text( "Triggered ajaxError handler." );
});

In the code above, if there will be any error in any ajax request then #log span will show error message

Yes we can include multiple versions of jQuery in same page.

There may be a situation when we have a jQuery plugin in application which is dependent on older version of jQuery but for our own jQuery code, we want to use latest version of jQuery. So due to this dependency we will have to use multiple version of jQuery.

Here is an example to use multiple version of jQuery:

<script type='text/javascript' src='js/jquery_1.9.1.min.js'></script>
	
<script type='text/javascript'>
   var $jq = jQuery.noConflict();
</script>
	
<script type='text/javascript' src='js/jquery_1.7.2.min.js'></script>

By this way, for your own jQuery code use "$jq", instead of "$" as "$jq" refers to jQuery 1.9.1, where "$" refers to 1.7.2.

The latest version of jQuery library (at the time of writing this article) is 1.11.3 or 2.1.4.

No. jQuery 2.0 has no support for IE 6, IE 7 and IE 8.

Source Map is mapping of minified version of jQuery against the un-minified version. Source map allows to debug minified version of jQuery library. Source map feature was release with jQuery 1.9.

With release of 1.9 version of jQuery, many deprecated methods were discarded and they are no longer available. But there are many sites in production which are still using these deprecated features and it's not easy to replace them overnight. So jQuery team provided with jQuery Migrate plugin that makes code written prior to 1.9 work with it.

So to use old/deprecated features, you need to provide reference of jQuery Migrate Plugin.

jQuery.browser property is used to write browser specific code. This property contains flags for the useragent, read from navigator.userAgent. This property was removed in jQuery 1.9.

The command $.ui.version returns jQuery UI version.

A plug-in is piece of code written in a standard JavaScript file . These files provide useful jQuery methods which can be used along with jQuery library methods. jQuery plugins are quite useful as its piece of code which is already written by someone and re-usable, which saves your development time.

jQuery UI provides a prebuilt set of functionality that gives your pages a polished, professional look and feel. It is an official plug-in with commonly used interface widgets, like slider controls, progress bars, accordions, etc.

jQuery is the core library. jQueryUI is built on top of it. If you use jQueryUI, you must also include jQuery.

jQuery Connect is a jquery plugin which enables us to connect a function to another function. It is like assigning a handler for another function. This situation happens when you are using any javascript plugins and you want to execute some function when ever some function is executed from the plugin. This we can solve using jquery connect function.

$.disconnect() function is used to disconnect a function to another function. It is opposite of $.connect().

Chaining is one of the most powerful feature of jQuery. Chaining provides the ability to chain multiple functions together to perform several operations in one line of code. It makes your code short and easy to manage. The chain starts from left to right. So left most will be called first and so on.

$(selector).fn1().fn2().fn3();

​$(document).ready(function(){
   $('#divTest').addClass('test');
   $('#divTest').css('color', 'blue');
   $('#divTest').fadeIn('slow');
});​

Using chaining, you can write above jQuery code like this:

​$(document).ready(function(){
   $('#divTest').addClass('test').css('color', 'blue').fadeIn('slow');
});​

Caching helps to increase performance and it can also be used in jQuery. If you are using an element in jQuery more than one time then you should cache that element.

For example:

$("#divTest").css("color", "red");
$("#divTest").html("Some Text Here!");
//Some more code for #divTest

In jQuery code given above, we are using #divTest multiple time. Whenever it will be used like this, jQuery will have to traverse through DOM to get that element. We can avoid this extra traversing by saving this div in a variable:

var $divTest = $("#divTest");
$divTest.css("color", "red");
$divTest.html("Some Text Here!");
//Some more code for #divTest

Now jQuery will not traverse again to find #divTest. We can user variable #divTest. In jQuery caching means saving jQuery selector in a variable and use that variable reference whenever required.

There may be many reasons for this:

• You have forgot to include the reference of jQuery library and trying to access jQuery.
• You have include the reference of the jQuery file, but name or path of referenced jQuery file is not correct.
• You have include the reference of the jQuery file, but it is after your jQuery code.
• The order of the scripts is not correct. For example, if you are using any jQuery plugin and you have placed the reference of the plugin js before the jQuery library then you will face this error.

You need to use follwing methods for encoding and decoding of url in jQuery:

You need to pass the complete url with parameterized value in the function. These functions will return you encoded/decoded url as a result.

You can use following code to disable browser back button:

window.history.forword(1);
   //or
window.history.forword(-1);

$(document).ready(function()
{
   $(this).bind("contextmenu"),function(e)
   {
      e.preventDefault();
   });
});

$(document).ready(function()
{
   $("#txtTest").bind("copy paste cut"),function(e)
   {
      e.preventDefault();
   });
});

By using code given above cut, copy and paste will be disabled on #txtTest textbox.