Sum of 2 fields using jquery

sum.js

$(document).ready(function() {
  $(".expenses").on('keyup change', calculateSum);
});

function calculateSum() {
  var $input = $(this);
  var $row = $input.closest('tr');
  var sum = 0;

  $row.find(".expenses").each(function() {
    sum += parseFloat(this.value) || 0;
  });

  $row.find(".expenses_sum").val(sum.toFixed(2));
}