I'm trying to implement a custom validator in JavaScript for my vb.net page. This validator should check if in a multichoice listbox there aren't any selected values, showing an error pop up if so.

The thing is, I want to do it client side, but in my 'validateFunction' function I only get the last selected (or unselected, if it was selected already) item. I know how to do it in code-behind code, but I want to do it client-side.

*aspx code:*

```
 <asp:ListBox ID="lbEdit" runat="server" SelectionMode="Multiple">
 </asp:ListBox>
 <asp:CustomValidator id="cvEdit" runat="server" Display="None" ControlToValidate="lbEdit" ClientValidationFunction="validateFunction"/>
 <ajax:ValidatorCalloutExtender runat="server" ID="vceEdit" TargetControlID="cvEdit" />

```

*JavaScript code:*

```
 function validateFunction(source, arguments) {
        var options = document.getElementById(source.controltovalidate).options;
            for (var i = 0; i < options.length; i++) {
                if (options[i].selected == true) {
                    args.IsValid = true;
                    return;
                }
            }
            args.IsValid = false;
 }

```

As I said, since last (un)selected item will be the only one selected in the 'options' array, the validating function will always return true... 

I thought of populating another array in another javascript function as the 'true selected array' and compare its values with the selected option each time the function fires.. but I think there should be a better way.

So... Is there a straight forward way to get ALL the selected items from a multichoice listbox in javascript?
['https://Stackoverflow.com/questions/46149981', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/7126334/']
Your question is a bit unclear, and your function seems working, but what I will answer here is the last part of your question *So... Is there a straight forward way to get ALL the selected items from a multichoice listbox in javascript?*

Try this js function

```
<script type="text/javascript">
        function validateFunction() {
            var options = document.getElementById('<% = this.lbEdit.ClientID %>').options;
            var selectedItems;
            for (var i = 0; i < options.length; i++) {
                if (options[i].selected == true) {
                    if (selectedItems) {
                        selectedItems = selectedItems + ";" + options[i].value;
                    }
                    else {
                        selectedItems = options[i].value;
                    }
                }
            }
            if (selectedItems) {
                alert(selectedItems);
                return true;
            }
            else {
                alert("No item was selected");
                return false;
            }
        }
    </script>

```

And this is the aspx code, I removed the validator

```
 <asp:ListBox ID="lbEdit" runat="server" SelectionMode="Multiple" >
 </asp:ListBox>
    <asp:Button ID="test" runat="server" Text="send"  OnClientClick="return validateFunction();"/>

```

In the developer tools of your browser you can see a detailed information about all the properties of your object

[![enter image description here](https://i.stack.imgur.com/ZC8Hh.png)](https://i.stack.imgur.com/ZC8Hh.png)
```
let a1 = [
{
    Selected:false,
},
{
    Selected:false
},
{
    Selected:false
}];

```

if (a1.some(i => i.Selected))
 console.log(true);
else
 console.log(false);

Maybe what you want