ASP.NET

function TestForDuplicates() {

      //Make an Arrary Values of the Textboxes
      var Texboxes = new Array(); // regular array (add an optional integer
      Texboxes[0] = document.getElementById("<%= txtUnitLen1.ClientID %>").value;      // argument to control array's size)
      Texboxes[1] = document.getElementById("<%= txtUnitLen2.ClientID %>").value;
      Texboxes[2] = document.getElementById("<%= txtUnitLen3.ClientID %>").value;
      Texboxes[3] = document.getElementById("<%= txtUnitLen4.ClientID %>").value;
      Texboxes[4] = document.getElementById("<%= txtUnitLen5.ClientID %>").value;
      Texboxes[5] = document.getElementById("<%= txtUnitLen6.ClientID %>").value;
      Texboxes[6] = document.getElementById("<%= txtUnitLen7.ClientID %>").value;
      Texboxes[7] = document.getElementById("<%= txtUnitLen8.ClientID %>").value;
      Texboxes[8] = document.getElementById("<%= txtUnitLen9.ClientID %>").value;
      Texboxes[9] = document.getElementById("<%= txtUnitLen10.ClientID %>").value;
      Texboxes[10] = document.getElementById("<%= txtUnitLen11.ClientID %>").value;
      Texboxes[11] = document.getElementById("<%= txtUnitLen12.ClientID %>").value;
      Texboxes[12] = document.getElementById("<%= txtUnitLen13.ClientID %>").value;
      Texboxes[13] = document.getElementById("<%= txtUnitLen14.ClientID %>").value;
      Texboxes[14] = document.getElementById("<%= txtUnitLen15.ClientID %>").value;
      Texboxes[15] = document.getElementById("<%= txtUnitLen16.ClientID %>").value;
      Texboxes[16] = document.getElementById("<%= txtUnitLen17.ClientID %>").value;
      Texboxes[17] = document.getElementById("<%= txtUnitLen18.ClientID %>").value;
      Texboxes[18] = document.getElementById("<%= txtUnitLen19.ClientID %>").value;
      Texboxes[19] = document.getElementById("<%= txtUnitLen20.ClientID %>").value;


      //+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
      var btn = document.getElementById("<%= btnComplete.ClientID %>");
      document.getElementById("<%= hidDuplicate.ClientID %>").value = findDuplicates(Texboxes);
      return false;
  }

protected void btnComplete_Click1(object sender, EventArgs e)
{


    Page.ClientScript.RegisterStartupScript(this.GetType(), "alert", "TestForDuplicates();", true);

    if (hidDuplicate.Value == null || hidDuplicate.Value == "")
    {

        Response.Write("<script>alert('There are no Duplicaets');</script>");
    }
    else
    {
        Response.Write("<script>alert('There are Duplicate Units: " + hidDuplicate.Value + "');</script>");

    }
}

<asp:Button ID="btnComplete" runat="server" 
                     Text="Complete" Width="83px" 
                      TabIndex="20" onclick="btnComplete_Click1" />

<asp:HiddenField ID="hidDuplicate" runat="server" />