update_totals.js

// Update subtotal and total amounts on checkout, considering fees
GrowDough.Behaviors.UpdateTotal = Essential.Behavior.extend({
  init: function() {},

  events: {
    'keyup': 'updateSubtotal'
  },

  updateSubtotal: function(e, force) {
    // Keys and events on which the behavior has to update totals
    var isNumber = e && ( (e.which >= 48 && e.which <= 57) || (e.which >= 96 && e.which <= 105) ),
      isBackSpace = e && e.which == 8,
      isDelete = e && e.which == 127,
      isClick = e && e.which == 1;

    if ( isNumber || isBackSpace || isDelete || isClick || force ) {
      // Update totals
    }
  }
});