How to run a vb.net code-behind sub from the 'blur' event in an input text box

I am developing a form where I need to validate some of the information the user enters. I would like to validate this information AS THE USER moves through the form.

So, i was thinking that I could call SUBS and/or FUNCTIONS using the OnBlur Event on the form fields I need to validate.

I am not sure how to do this. I really would like to be able to call some code-behind routines instead of using javascript. In fact, JS is out of the question for the routines themselves, but I would be willing to use it to call the vb.net routines if need be.

Is this even possible?

You will see in the code example below that i am using an asp:image button that fires the validation routine using the onclick event. I would like to apply that same logic the form's input "OnBlur" event.

Thank you in advance for your reply.

<label for="txbCustomerCode">Customer Code: </label>
        <input id="txbCustomerCode" type="text" size="15" name="txbCustomerCode" runat="server" tabindex="3" title="Your Four Season's account number. You can find this number on an invoice, or contact your Sales Representative." />
        <asp:ImageButton CssClass="validation" ImageUrl="Images/Warning-20.png" runat="server" OnClick="subCheckCustomerCode" ID="imgCustomerCodeValidate" />
        <p class="labelinfo">Your Four Season's account number. You can find this number on an invoice, or contact your Sales Representative.</p>
        <br class="clear" />

=================================================

    Protected Sub subCheckCustomerCode(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles imgCustomerCodeValidate.Click
        Dim strCustomerCode As String = "123456"
        Dim strCustomerCodeText As String = txbCustomerCode.Value

        If strCustomerCodeText = strCustomerCode Then
            imgCustomerCodeValidate.Attributes("src") = "Images/Checkmark-20.png"
        Else
            imgCustomerCodeValidate.Attributes("src") = "Images/Error-20.png"
        End If

    End Sub

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