How to get the CheckBoxlist Value using Javascript?

Create a new control by the following steps.

Step 1:
Create a class library project

using System;
using System.Collections.Generic; 
using System.Text; 
using System.Globalization; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
namespace CheckBoxListExCtrl 
{ 
public class CheckBoxListExCtrl :CheckBoxList, IRepeatInfoUser 
{  
 void IRepeatInfoUser.RenderItem(ListItemType itemType, int repeatIndex, RepeatInfo repeatInfo, HtmlTextWriter writer) 
 {
     writer.WriteBeginTag("input"); 
     writer.WriteAttribute("type", "checkbox"); 
     writer.WriteAttribute("name", UniqueID); 
     writer.WriteAttribute("id", ClientID + "_" + repeatIndex.ToString(NumberFormatInfo.InvariantInfo)); 
     writer.WriteAttribute("value", Items[repeatIndex].Value); 
     System.Web.UI.AttributeCollection attrs = Items[repeatIndex].Attributes;      foreach (string key in attrs.Keys) 
     {
        writer.WriteAttribute(key, attrs[key]);
     }
     writer.Write(">"); 
     writer.Write(Items[repeatIndex].Text);
  }
} 
} 

Step 2:
Build it into a .dll file,and add it to toolbox of vs.net . then you can use it from your project:

Step 3:
When we add this control into .aspx page following code is genereted .

<asp:checkboxlistexctrl id="CheckBoxListExCtrl111" runat="server" RepeatDirection="Horizontal"></asp:checkboxlistexctrl>

Step 4:
From the Code behind we have to write code to bind the CheckBoxListExCtrl control.

protected void PopulateCheckBoxListExCtrl() 
{
   CheckBoxListExCtrl.DataSource = DtRecords;//DataTable DtRecords from DB
   CheckBoxListExCtrl.DataTextField ="Column1"; 
   CheckBoxListExCtrl.DataValueField ="Column2"; 
   CheckBoxListExCtrl.DataBind();
}

Step 5:
Then We can get the checkbox list value easily by
document.getElementByID("CheckBoxListExCtrl").value