Validating RadioButtonList and DropDownList Using JavaScript

In this article we learn how to validate a RadioButtonList and a DropDownList using JavaScript in ASP.NET. JavaScript provides a way to validate a form's data on the client's computer before sending it to the web server. If we try to perform all the validation on the server side then naturally the server is will take time to process the details and finally it will give a response to the client. In some cases, some of the data that had been entered by the client was in the wrong form or was simply missing. The server would then need to send all the data back to the client and request that the form be resubmitted with the correct information. So this is not an efficient way to do the validation. So we use JavaScript that validates at the client side.

To validate RadioButtonList in JavaScript

function getCheckedRadioButton() {

    var radio = document.getElementsByName("RadioButtonList1"); //Client ID of the RadioButtonList1                          

    for (var i = 0; i < radio.length; i++) { 

       if (radio[i].checked) { // Checked property to check radio Button check or not

       alert("Radio button having value " + radio[i].value + " was checked."); // Show the checked value

       return true;

       }

    }   

  alert("Not checked any radio button");      // if not checked any RadioButton from the RadioButtonList  

}

 

The following is the source code for the design of our "Default.ASPX" page:

 

<asp:RadioButtonList ID="RadioButtonList1" runat="server">

<asp:ListItem Value="Java">Java</asp:ListItem>

<asp:ListItem Value="Dot Net">Dot Net</asp:ListItem>

<asp:ListItem Value="JavaScript">JavaScript</asp:ListItem>

<asp:ListItem Value="jQuery">jQuery</asp:ListItem>

 </asp:RadioButtonList>

 <br />

 <br />       

 <asp:Button ID="submitForm" runat="server" OnClientClick="getCheckedRadioButton()"

  Text="Submit" />                                                  

      

Now to see the output press F5 to execute.

 

Output

 

 

Now click on the Button control without checking a radio button.

 

 

Now select a radio button and click on the Button.

 

To validate DropDownList in JavaScript

function validateDropList() {

    if (document.getElementById("<%=DropDownList1.ClientID%>").value == "")  //Client ID of the DropDownList

     {

         alert("Please select a country form DropDownList");

          return false;

     }

     else

         return true;
}

The following is the source code for the design of our ".ASPX" page:

 

<div>

<asp:DropDownList ID="DropDownList1" runat="server">

   <asp:ListItem Value="">select</asp:ListItem>

   <asp:ListItem Value="ind">India</asp:ListItem>

   <asp:ListItem Value="pak">PAK</asp:ListItem>

   <asp:ListItem Value="usa">US</asp:ListItem>

   <asp:ListItem Value="uae">UAE</asp:ListItem>

   </asp:DropDownList>

   <br />

   <br />

   <asp:Button ID="submitForm" runat="server" OnClientClick="validateDropList()" Text="Submit" />

 </div>

 

Now press F5 to execute it.

 

Output

 

 

Now click on the Button control without selecting a country from the DropDownList.