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jQuery Selectors in asp.net 2.0 - 3.5

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Steve Krile
Process-first, software second.
Just a quick little trick I learned recently.  Now that I'm using jQuery with abandon in my asp.net applications, I have grown tired of the following syntax:

     
$("#<%=MyInputField.ClientID%>")

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I suppose it just offends my sense of decency to put inline VBScript on an .aspx page.  So, I started looking at the jQuery selector core and found a nice little gem.  Now, it's not perfect, and there are certainly ways for it to fail, but in general I've found that if you feed the following the proper context, it always works:

Given an html element like this:

       
<asp:TextBox runat="server" id="MyInputField" />

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Which gets rendered like this (since I use Master pages)

     
<input type="text" id="c100_Panel1_MyInputField" />

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You can select the input field like this:

     
$("input[id$=MyInputField]");

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The great part about this from my point of view is that my jQuery markup will match my .net markup.  This leads to the ability to loop through jQuery objects and do a bunch of things without needing to first determine the .net rendered client ID.  Also, I can use .net runat=server objects with jQuery and they will work together.  In other words, if I want to take some fields in an asp:Panel and paint them pretty or use JSON to complete them, I can do that with jQuery.  But if I want to then take the values of those fields and do server-side work with them when a button is clicked, the value of those fields will be available in my .vb file as part of the page controls.

If you are concerned about controls with ID's that match across multiple parts of you page, you could narrow the scope of the selector like this:

HTML:

<asp:Panel runat="server" id="MyPanel1">
    <asp:TextBox runat="server" id="MyInput" />
</asp:Panel>

<asp:Panel runat="server" id="MyPanel2">
    <asp:TextBox runat="server" id="MyInput2" />
</asp:Panel>

This above setup would cause problems with my original design because both MyInput and MyInput2 would match the selector.  So, we could do a selector like this:

$("input[id$=MyInput]","div[id$=MyPanel1]")

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This works based on jQuery's selector model $([object],[object context]).  That object context part is optional and many times not necessary, but if you want jQuery to stick to one section of your document, this is a handy way to do it...and we can use the .net Panel object because we are referring to it with the id$=MyPanel1 trick.

Pretty handy stuff.
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Author:Steve Krile
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Expert Comment

by:Kevin Cross
skrile, I have read your "Pimp Exchange" article a number of times now and smile EVERY time I read the title by the way...I had not yet read this, though, for whatever reason. Very nice tip/trick. You have my Yes vote above!
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Author Comment

by:Steve Krile
Thank.  Just emerging myself in Knockoutjs now.  Mind is swelling.
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