You can do something like this adding the 'script' tag at the bottom of the view.

        <script>
              $("#field1",).on('change', function(){
                var val2 = $("#field2").val(),
                    val1 = $(this).val();
                if(val2!=0)
                {
                    var sum = parseInt(val1) + parseInt(val2);
                    $(this).val(sum);
                }
            });
        </script>

Hope this helps.

Daniel

I mean, fix this problem for "Laravel Nova". The views are make by Node.

Your "problem" doesnt have anything to do with Laravel Nova or the views made by Node, The user interaction is handled by javascript / jQuery.