How to manual validate in Form

I need to validate onSubmit of form if the variable have value then complete else ignore event click and hide 'please wait' message

I think the code below was working in joget v6 but I need the updated for Joget DX
$(document).ready(function(){
  $("#assignmentComplete").click(function() {
     var url=$("#url").val();
     If(url==null || url==""){

        event.preventDefault();
        $(".blockUI").remove();
        }
     });
});