I'm using two RadDatePicker controls showing Date From and Date To and need to make sure that before submitting the form, at least one of the date is provided.

I have a JavaScript code checking to make sure that the user provides at least one date value:

function validateDates(sender, eventArgs) {

    var datePicker1 = $find("<%=RadDatePicker1.ClientID %>");
    var datePicker2 = $find("<%=RadDatePicker2.ClientID %>");


    if (datePicker1.get_selectedDate() == null && datePicker2.get_selectedDate() == null) 
    {
        alert("At least one date should be selected");
        eventArgs.set_cancel(true);
    }

       //alert(datePicker1.lastSetTextBoxValue.value);
       //return false;
}

That part works.

However, a user can also type a string in which case, it will also fails with the same message, because get_selecteddate() method also returns null.

But, what I want is to actually check if the value entered is of a date format and display the corresponding message to the user.

So, in my case, I would need to use a validation for the correct date format as well.

I noticed that when Telerik DatePicker is rendered, it builds the following html sections:

<input id="ctl00_Contentplaceholder2_RadDatePicker1_dateInput" name="ctl00$Contentplaceholder2$RadDatePicker1$dateInput" class="riTextBox riError" type="text" style="">

<input id="ctl00_Contentplaceholder2_RadDatePicker1_dateInput_ClientState" name="ctl00_Contentplaceholder2_RadDatePicker1_dateInput_ClientState" type="hidden" autocomplete="off" value="{&quot;enabled&quot;:true,&quot;emptyMessage&quot;:&quot;&quot;,&quot;validationText&quot;:&quot;&quot;,&quot;valueAsString&quot;:&quot;&quot;,&quot;minDateStr&quot;:&quot;1980-01-01-00-00-00&quot;,&quot;maxDateStr&quot;:&quot;2099-12-31-00-00-00&quot;,&quot;lastSetTextBoxValue&quot;:&quot;hhh&quot;}">

From that html I see that when a string is entered into a DatePicker, its input element gets assigned a css class called riError and its lastSetTextBoxValue has a string I entered.

So, I can assume, I can use those two properties to improve my validation logic.

How can I do that? Any ideas?