Accepting 5digit numder using javascript code

<asp:TextBox ID="TextBox1" Width="250Px" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" OnClientClick="javascript:validateZipCode()" Text="Button" />
JavaScript Code:
<script type="text/javascript">
function validateZipCode()
{
var zipCodePattern = /^\d{5}$|^\d{5}-\d{4}$/;
var elementValue=document.getElementById('<%=TextBox1.ClientID %>').value
if (elementValue.search(zipCodePattern) == -1)
{
alert('please enter valid 5 dit num')
}
}
</script>