title: JQuery $( returning null
body: <p>I am having problems with my JQuery returning null.</p>
  
  <p>Here is my JQuery (which is contained in a .js)....</p>
  
  <pre><code>$(document).ready(function() {        
  var chkBox = $("#gvEntryPoints input[id$='cbxIncludeAll']");        
  chkBox.click(function() {                 
      $("#gvEntryPoints input[type='checkbox']").attr('checked', chkBox.is(':checked'));
  });        
  
  // To deselect CheckAll when a GridView CheckBox is unchecked        
  $("#gvEntryPoints INPUT[type='checkbox']").click(function(e) {            
      if (!$(this)[0].checked) {                
          chkBox.attr("checked", false);            
      }        
  });    
  </code></pre>
  
  <p>}</p>
  
  <p>It appears the chkBox never gets assigned and therefore there is never a click event that is assigned.</p>
  
  <p>Here is my HTML...</p>
  
  <pre><code>&lt;asp:GridView CssClass="GridView" ID="gvEntryPoints" runat="server" AutoGenerateColumns="false"&gt;
              &lt;Columns&gt;
                  &lt;asp:TemplateField Visible="false"&gt;
                      &lt;ItemStyle CssClass="GridView_Item" /&gt;
                      &lt;ItemTemplate&gt;
                          &lt;asp:Label runat="server" ID="lblEntryPointListItemId" Text='&lt;%# Eval("EntryPointListItemId") %&gt;'/&gt;
                      &lt;/ItemTemplate&gt;
                  &lt;/asp:TemplateField&gt;
                  &lt;asp:TemplateField Visible="false"&gt;
                      &lt;ItemStyle CssClass="GridView_Item" /&gt;
                      &lt;ItemTemplate&gt;
                          &lt;asp:Label runat="server" ID="lblEntryPointId" Text='&lt;%# Eval("EntryPointId") %&gt;'/&gt;
                      &lt;/ItemTemplate&gt;
                  &lt;/asp:TemplateField&gt;
                  &lt;asp:TemplateField HeaderText="Include"&gt;
                      &lt;ItemStyle CssClass="GridView_Item" /&gt;
                      &lt;HeaderTemplate&gt;
                          &lt;asp:CheckBox runat="server" ID="cbxIncludeAll" CssClass="label" Checked="true" Text="Include&lt;br/&gt;All" TextAlign="Left" /&gt;
                      &lt;/HeaderTemplate&gt;
                      &lt;ItemTemplate&gt;
                          &lt;asp:CheckBox runat="server" ID="cbxEPInclude" name="EPInclude" CssClass="EPCheckBox" Checked="true" /&gt;
                      &lt;/ItemTemplate&gt;
                  &lt;/asp:TemplateField&gt;
              &lt;/Columns&gt;
          &lt;/asp:GridView&gt;
  </code></pre>
  
  <p>My HTML lies within an .ascx.  The .ascx is contained on a .aspx content page.  I have the JQuery library included on the Master page (I have tried in the Head, top of the body, and bottom of the body).</p>