title: how to disable previous date in calendar extender in javascript
body: <p>I want to disallow the previous dates in calendar extender. I'm able to show pop up when previous date is selected, but textbox is not clearing.</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
      function checkDate(sender, args) {
          if (sender._selectedDate &lt; new Date()) {
              alert("You cannot select a day earlier than today!");
              sender._selectedDate = new Date();
              sender._textbox.set_Value(sender._selectedDate.format(sender._format))
              document.getElementById("txtNextFollowupDate").value = "";//want to make empty
         }
      }
  &lt;/script&gt;
  
  &lt;tr&gt;
      &lt;td&gt;&lt;asp:Label ID="Label18" Text="Next Follow up date" runat="server"&gt;&lt;/asp:Label&gt;&lt;/td&gt;
      &lt;td&gt;:&lt;/td&gt;
      &lt;td&gt;
          &lt;asp:TextBox runat="server" ID="txtNextFollowupDate" /&gt;
          &lt;asp:CalendarExtender ID="CalendarNextFollowUpDate" runat="server" TargetControlID="txtNextFollowupDate" OnClientDateSelectionChanged="checkDate" &gt; &lt;/asp:CalendarExtender&gt;
      &lt;/td&gt;
  &lt;/tr&gt;
  </code></pre>