jQuery add event handler to dynamically created element

The following example, allows us to dynamically create new list item (li), attach a click event handler and add it to the unordered list (ul). This happens when you click "Add a New List Item" button. The problem with this approach is that we are binding a click event handler to every list item. This means if you have 500 list items, then there will be 500 event handlers in the memory and this may negatively affect the performance of your application. 
<html>
<head>
    <title></title>
    <script src="jquery-1.11.2.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $('li').on('click', function () {
                $(this).fadeOut(500);
            });

            $('#btnAdd').on('click', function () {
                var newListItem = $('<li>New List Item</li>').on('click', function () {
                    $(this).fadeOut(500);
                });

                $('ul').append(newListItem);
            });
        });
    </script>
</head>
<body style="font-family:Arial">
    <input id="btnAdd" type="button" value="Add a New List Item" />
    <ul>
        <li>List Item</li>
        <li>List Item</li>
    </ul>
</body>
</html>

A better way of doing the same from a performance standpoint is shown below. In this example, the click event handler is attached to the listitem (li) parent element (ul). Even if you have 500 list items, there is only one click event handler in memory. 

So how does this work
1. When you click on a list item (li), the event gets bubbled up to its parent (ul) as the list item (li) does not have an event handler 
2. The bubbled event is handled by the the parent (ul) element, as it has a click event handler.
3. When a new list item is added dynamicaly, you don't have to add the click event handler to it. Since the newly created list item (li) is added to the same parent element (ul), the click event of this list item also gets bubbled upto the same parent and will be handled by it. 

<html>
<head>
    <title></title>
    <script src="jquery-1.11.2.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $('ul').on('click', 'li', function () {
                $(this).fadeOut(500);
            });

            $('#btnAdd').on('click', function () {
                $('ul').append('<li>New List Item</li>');
            });
        });
    </script>
</head>
<body style="font-family:Arial">
    <input id="btnAdd" type="button" value="Add a New List Item" />
    <ul>
        <li>List Item</li>
        <li>List Item</li>
    </ul>
</body>
</html>

Comments

Post a Comment

Popular posts from this blog

Drag and Drop multiple File upload using jQuery AJAX in ASP.Net using C# and VB.Net

Multiple files such as Image, PDF, Word, Excel, etc. and also large Music and Video files such as MP3 and MP4 will be easily uploaded by simple Drag and Drop of files in HTML5 supported browsers using jQuery and AJAX in ASP.Net. This article makes use of the jQuery FileDrop plugin which makes use of Generic HTTP Handlers for uploading files with Drag and Drop using jQuery and AJAX in ASP.Net. In this article I will explain with an example, how to upload multiple files with Drag and Drop in HTML5 supported browsers using jQuery and AJAX in ASP.Net using C# and VB.Net. Multiple files such as Image, PDF, Word, Excel, etc. and also large Music and Video files such as MP3 and MP4 will be easily uploaded by simple Drag and Drop of files in HTML5 supported browsers using jQuery and AJAX in ASP.Net. This article makes use of the  jQuery FileDrop  plugin which makes use of Generic HTTP Handlers for uploading files with Drag and Drop using jQuery and AJAX in ASP.Net.  ...
Read more

jQuery dynamic menu from database in asp.net

Step 1 : Create SQL Server table and insert menu data  Create table tblMenu (     Id int primary key identity,     MenuText nvarchar(30),     ParentId int foreign key references tblMenu(Id),     Active bit ) Go Insert into tblMenu values('USA', NULL, 1) Insert into tblMenu values('India', NULL, 1) Insert into tblMenu values('UK', NULL, 1) Insert into tblMenu values('Australia', NULL, 1) Insert into tblMenu values('Virginia', 1, 1) Insert into tblMenu values('Maryland', 1, 1) Insert into tblMenu values('AP', 2, 1) Insert into tblMenu values('MP', 2, 1) Insert into tblMenu...
Read more

Automatically send Birthday email using C#.Net

In order to automatically send Birthday email daily at particular time, a Windows Service will be created which will run daily at the particular time and will automatically send Birthday emails using C#.Net. In this article the Windows Service will execute a Task daily at a specific time. The Task is to fetch all records of Students who have a Birthday today. Such students will receive an email containing Birthday wishes automatically by the Windows Service. Config:- < appSettings >     < add  key  = " Mode "  value  = " Daily "  />     < add  key  = " IntervalMinutes "  value  = " 1 "  />     < add  key  = " ScheduledTime "  value  = " 17:43 "  /> </ appSettings > < connectionStrings >     < add  name = " constr "  connectionString = " Data Source=.\SQL2008R2;Initial Catalog=S...
Read more