I'm working on a custom module for POS. When i set a current screen, i can't back on the previous. Here is the error i got:

Software Error (user interface)
Uncaught TypeError: this.current_screen.close is not a function 
http://localhost/web/js/web.assets_backend/5b337eb:4502 

This is the code i wrote

function pos_ordonnance(instance, module){
  var QWeb = instance.web.qweb;
  module.PosWidget.include({
    build_widgets: function(){
      var self = this;
      this._super();
      // -------- Ordonnance screen and his selector ---------
      this.ordonnance_screen = new module.OrdonnanceListWidget(this,{});
      this.ordonnance_screen.appendTo(this.$('.screens'));
      this.screen_selector.add_screen('ordonnances',this.ordonnance_screen);
  });
  module.OrdonnanceButtonWidget = module.PosBaseWidget.extend({
    template: 'OrdonnanceButtonWidget',
    init: function(parent, options){
      this._super(parent);
    }
  });
  module.OrdonnanceListWidget = module.PosBaseWidget.extend({
    template:'OrdonnanceListWidget',
    init: function(parent, options) {
      this._super(parent);
    },
    renderElement: function() {
      var self = this;
      this._super();
      self.afficherOrdonnance()
      self.get_ordonnances()
    },
    afficherOrdonnance: function(){
      var button = $(QWeb.render('OrdonnanceButtonWidget'));
      button.appendTo($('.control-buttons'));
      $('.control-buttons').removeClass('oe_hidden');
      $('.control-buttons').addClass('mypad');
      button.click(function(){
        $(QWeb.render('OrdonnanceListWidget'));
        $('.ordonnance-list-container').removeClass('oe_hidden');
        self.pos_widget.screen_selector.set_current_screen('ordonnances');
      })
    },
    get_ordonnances: function(){
      var self = this;
      var ordonnance_list = [];
      var loaded = new instance.web.Model("oeh.medical.prescription");
      loaded.call("get_ordonnances_to_pos", {context: new instance.web.CompoundContext()})
      .then(function(ordonnance){
        for(var i = 0, len = ordonnance['result'].length; i < len; i++){
          var content = $('.ordo-content-tbody').html();
          var ordo_prescription = ordonnance['result'][i]['name']
          var ordo_patient = ordonnance['result'][i]['patient'][1]
          var ordo_date = ordonnance['result'][i]['date']
          var ordo_doctor = ordonnance['result'][i]['doctor'][1]
          var new_prescription = '<td class=ordo-prescription\'' + ordo_prescription + '\'>' + ordo_prescription + '</td>\n';
          var new_patient = '<td class=ordo-patient\'' + ordo_patient + '\'>' + ordo_patient + '</td>\n';
          var new_date = '<td class=ordo-date\'' + ordo_date + '\'>' + ordo_date + '</td>\n';
          var new_doctor = '<td class=ordo-doctor\'' + ordo_doctor + '\'>' + ordo_doctor + '</td>\n';
          var new_tr_prescription = '<tr class=ordo prescription-tr\'' + ordo_prescription + '\'>' + new_prescription + new_patient + new_date + new_doctor + '</tr>\n';
          $('.ordo-content-tbody').html(content + new_tr_prescription);
        }
      });
    }
  });
}
(function(){
    var _super = window.openerp.point_of_sale;
    window.openerp.point_of_sale = function(instance){
        _super(instance);
        var module = instance.point_of_sale;
        pos_ordonnance(instance, module);
    }
})();