Using single ClientValidationFunction for similar validations using custom validator

Here is an example of how to write a common client validation function while using similar kind of validations on more than one asp.net control.

This example is showing how to validate two drop down list using a single javascript function for required
ASP.NET Markup

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1. <asp:DropDownList ID="ddlCountry" runat="server" AutoPostBack="True"
2. onselectedindexchanged="ddlCountry_SelectedIndexChanged" CausesValidation="false">
3. asp:DropDownList>
4. <asp:CustomValidator ID="cvCountry" runat="server" ControlToValidate="ddlCountry"
5. EnableClientScript="true" ValidationGroup="REG" Display="None" ErrorMessage="Country is required" Text=" "
6. ClientValidationFunction="validateCbo">asp:CustomValidator>
7. <asp:DropDownList ID="ddlState" runat="server">
8. asp:DropDownList>
9. <asp:CustomValidator ID="cvState" runat="server" ControlToValidate="ddlState"
10. EnableClientScript="true" ValidationGroup="REG" Display="None" ErrorMessage="State is required" Text=" "
11. ClientValidationFunction="validateCbo">asp:CustomValidator>

Javascript client validation function:

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1. function validateCbo(source, args) {
2. var ddl = null;
3. if(source.controltovalidate.indexOf('Country')>-1)
4. ddl = document.getElementById('');
5. else
6. ddl = document.getElementById('');
7. if (ddl != null) {
8. args.IsValid = !(ddl.options[ddl.selectedIndex].value == 0);
9. }
10. else
11. args.IsValid = true;
12. }