Sharing best interview questions and answers on Jquery.
jQuery is a lightweight JavaScript library which gives a quick and simple method for HTML DOM traversing and manipulation, its event handling, its client-side animations, and so on. One of the best features of jQuery is that jQuery supports an efficient way to implement AJAX applications because of its lightweight nature and make normalize and efficient web programs.
Document.ready() function is different from body onload() function because off 2 reasons.
Features of Jquery
There are 3 types of selectors in Jquery
There are many advantages of JQuery. Some of them are :
jQuery is very compact and well-written JavaScript code that increases the productivity of the developer by enabling them to achieve critical UI functionality by writing very less amount of code.
It helps to
Other advantages of jQuery are
There are three building blocks to select the elements in a web document.
1. Select elements by tag name
Example
$(div)
It will select all the div elements in the document.
2. Select elements by ID
Example
$(“#abc”)
It will select single element that has an ID of abc.
3. Select elements by Class
Example
$(“.xyzClass”)
It will select all the elements having class xyzClass.
In jQuery, there is two way to change the width of an element. One way is using .css(‘width’) and other way is using .width().
For example
$('#mydiv').css('width','300px');
$('#mydiv').width(100);
The bind() method will not attach events to those elements which are added after DOM is loaded while live() and delegate() methods attach events to the future elements also.
The difference between live() and delegate() methods is live() function will not work in chaining. It will work only on an selector or an element while delegate() method can work in chaining.
For example
$(document).ready(function(){
$("#myTable").find("tr").live("click",function(){
alert($(this).text());
});
});
Above code will not work using live() method. But using delegate() method we can accomplish this.
$(document).ready(function(){
$("#dvContainer")children("table").delegate("tr","click",function(){
alert($(this).text());
});
});
The param() method is used to represent an array or an object in serialize manner.
While making an ajax request we can use these serialize values in the query strings of URL.
Syntax:
$.param(object | array, boolValue)
“object | array” specifies an array or an object to be serialized.
“boolValue” specifies whether to use the traditional style of param serialization or not.
Example
personObj=new Object();
empObject.name="Ravi";
empObject.age="28";
empObject.dept="IT";
$("#clickme").click(function(){
$("span").text($.param(empObject));
});
It will set the text of span to “name=Ravi&age=28&dep=IT”
jQuery .size() method returns number of element in the object. But it is not preferred to use the size() method as jQuery provide .length property and which does the same thing. But the .length property is preferred because it does not have the overhead of a function call.
$(document).ready(function(){
$('#clickme').click(function(){
alert($(this).text());
alert(this.innerText);
});
});
this and $(this) references the same element but the difference is that “this” is used in traditional way but when “this” is used with $() then it becomes a jQuery object on which we can use the functions of jQuery.?
In the example given, when only “this” keyword is used then we can use the jQuery text() function to get the text of the element, because it is not jQuery object. Once the “this” keyword is wrapped in $() then we can use the jQuery function text() to get the text of the element.
Ajax allows the user to exchange data with a server and update parts of a page without reloading the entire page. Some of the functions of ajax are as follows:
$.ajax(): This is considered to be the most low level and basic of functions. It is used to send requests . This function can be performed without a selector.
$.ajaxSetup(): This function is used to define and set the options for various ajax calls.
For example.
$.ajaxSetup({
"type":"POST",
"url":"ajax.php",
"success":function(data){
$("#bar")
.css("background","yellow")
.html(data);
}
});Shorthand ajax methods: They comprise of simply the wrapper function that call $.ajax() with certain parameters already set.
$.getJSON(): this is a special type of shorthand function which is used to accept the url to which the requests are sent. Also optional data and optional callback functions are possible in such functions.
.remove() is faster than .empty() or .detach() method.
Syntax:
$(selector).empty(); $(selector).remove(); $(selector).detach();
There are two ways to handle this issue:
Use of event delegation: The event delegation technique works on principle by exploiting the event bubbling. It uses event bubbling to capture the events on elements which are present anywhere in the domain object model. In jquery the user can make use of the live and die methods for the events delegation which contains a subset of event types.
For example. handling even delegation, handling of clicks on any <a> element:
$('#mydiv').click(function(e){
if( $(e.target).is('a') )
fn.call(e.target,e);
});
$('#mydiv').load('my.html')
Event rebinding usage: When this method is used it requires the user to call the bind method and the added new elements.
$('a').click(fn);
$('#mydiv').load('my.html',function(){
$('#mydiv a').click(fn);
});
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