asp.net textbox with java script problem
<p>I'm trying to check if asp.net textbox is empty or not using java script.
my code working ok but if 
I enter only numbers will conder it empty so I have either enter letters and numbers or only letters.</p>

<p>Please advice.</p>

<p>here is my code</p>

<pre><code> &lt;script type="text/javascript"&gt;
function check(){
  var txt = document.getElementById('&lt;%=txt.ClientID%&gt;').value;

              //(isNaN(cmbStateHome) == false

              if (isNaN(txt) == false) {
                  alert("Please enter some thing.");

              }
              else {alert("ok");}
          }
}
&lt;/script&gt; 


 &lt;asp:TextBox ID="txt" runat="server"&gt;&lt;/asp:TextBox&gt;
                &lt;asp:TextBox ID="txtZipCodeHome" runat="server" Style="top: 361px; left: 88px; position: absolute;

&lt;asp:LinkButton ID="LinkButton1" runat="server" OnClientClick="check()"&gt;LinkButton&lt;/asp:LinkButton&gt;
</code></pre>
