Untitled

<span>
<checkbox><label></br>
<checkbox><label></br>
<checkbox><label></br>
</span>

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="RealtimeCheckBoxListFiltering.Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title></title>
  <script type="text/javascript">
    window.onload = function () {
      var tmr = false;
      var labels = document.getElementById('cblItem').getElementsByTagName('label');
      var func = function () {
        if (tmr)
          clearTimeout(tmr);
        tmr = setTimeout(function () {
          var regx = new RegExp(document.getElementById('inputSearch').value);
          for (var i = 0, size = labels.length; i < size; i++)
            if (document.getElementById('inputSearch').value.length > 0) {
              if (labels[i].textContent.match(regx)) setItemVisibility(i, true);
              else setItemVisibility(i, false);
            }
            else
              setItemVisibility(i, true);
        }, 500);

        function setItemVisibility(position, visible)
        {
          if (visible)
          {
            labels[position].style.display = '';
            labels[position].previousSibling.style.display = '';
            if (labels[position].nextSibling != null)
              labels[position].nextSibling.style.display = '';
          }
          else
          {
            labels[position].style.display = 'none';
            labels[position].previousSibling.style.display = 'none';
            if (labels[position].nextSibling != null)
              labels[position].nextSibling.style.display = 'none';

          }
        }
      }

      if (document.attachEvent) document.getElementById('inputSearch').attachEvent('onkeypress', func);  // IE compatibility
      else document.getElementById('inputSearch').addEventListener('keydown', func, false); // other browsers
    };
  </script>
</head>
<body>
  <form id="form1" runat="server">
  <table>
    <tr>
      <td>
        <asp:TextBox runat="server" ID="inputSearch" ClientIDMode="Static" />
      </td>
    </tr>
    <tr>
      <td>
        <asp:CheckBoxList runat="server" ID="cblItem" ClientIDMode="Static" RepeatLayout="Flow" />
      </td>
    </tr>
  </table>
  </form>
</body>
</html>

using System;
using System.Collections.Generic;

namespace RealtimeCheckBoxListFiltering
{
    public partial class Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            cblItem.DataSource = new List<string>() { "qwe", "asd", "zxc", "qaz", "wsx", "edc", "qsc", "esz" };
            cblItem.DataBind();
        }
    }
}

var tmr = false;
var labels = document.getElementsByTagName('label')
var func = function() {
    if (tmr) clearTimeout(tmr);
    tmr = setTimeout(function () {
        var regx = new Regex(inputVal); /* Input value here */
        for(var i = 0, size = labels.length; i < size; i++) {
            if(regx.match(labels[i].textContent || labels[i].innerText)) labels[i].style.display = 'block';
            else labels[i].style.display = 'none';
        }
    }, 100);
}
if (document.attachEvent) inputField.attachEvent('onkeypress', func);
else inputField.addEventListener('keypress', func, false);