Js file  it dose not display the button in  pos 

 odoo.define('point_of_sale.pos_create_bo_2', function (require) {
var _t = instance.web._t;
var QWeb = instance.web.qweb;

var round_di = instance.web.round_decimals;
var round_pr = instance.web.round_precision;

instance.point_of_sale.ProductScreenWidget = instance.point_of_sale.ProductScreenWidget.extend({
init: function() {
this._super.apply(this, arguments);
},
start:function(){
var self = this;
this._super();
// on récupère le pos
pos = self.pos;
picking_type_id = pos.config.picking_type_id[0];
console.log(picking_type_id);

selectedOrder = self.pos.get('selectedOrder');
console.log('selectedOrder: '+selectedOrder);
function DO_Stuff(customer_id, orderLines, mylocation_id, picking_type_id, commentaire, montanttaxes) {
(new instance.web.Model('stock.picking')).get_func('create_back_order')(orderLines, customer_id, mylocation_id, picking_type_id, commentaire, montanttaxes)
.pipe(_.bind(function(res) {
if (res) {
for (i = 0; i <= currentOrderLines.length + 1; i++) {
currentOrderLines.each(_.bind(function(item) {
selectedOrder.removeOrderline(item);
}, this));
}
for (i = 0; i <= currentOrderLines.length + 1; i++) {
currentOrderLines.each(_.bind(function(item) {
selectedOrder.removeOrderline(item);
}, this));
}
selectedOrder.set_client();
var res_mess = _t('Bon de retour créé: ' + res[0] + '');

var error_dialog = new instance.web.Dialog(this, {
size: 'medium',
buttons: [{text: _t("Close"), click: function() { error_dialog.$el.modal('hide'); }}],
}).open();
error_dialog.$el.append('' + res_mess + '');
return;
}
else {
return alert('Une erreur est survenue pendant la création du bon de retour !');
}
}, self));
}
$("#create_bo").click(function() {
selectedOrder = pos.get('selectedOrder');
console.log('total taxes'+ selectedOrder.getTax());
totaltaxes = selectedOrder.getTax();
currentOrderLines = selectedOrder.get('orderLines');
orderLines = [];
currentOrderLines.each(_.bind(function(item) {
return orderLines.push(item.export_as_JSON());
}, this));

var customer_id = selectedOrder.get_client() && selectedOrder.get_client().id || '';
// on récupère du stock de destination
mylocation_id = 19;

if (orderLines.length === 0) {
return alert('Veuillez choisir un produit !');
}
if (!customer_id) {
return alert('Veuillez choisir un client !');
}
var error_dialog = new instance.web.Dialog(this, {
size: 'medium',
buttons: [{text: _t("Valider"), click: function() { var commentaire = document.getElementById('txtcom').value; DO_Stuff(customer_id, orderLines, mylocation_id, picking_type_id, commentaire, totaltaxes); error_dialog.$el.modal('hide'); }}],
}).open();
error_dialog.$el.append('