barcode_purchase_order/views/template.xml

<openerp>
    <data>
        <template id="barcode_purchase_order.assets_backend" name="barcode_purchase_order_assets" inherit_id="eiru_assets.assets">
            <xpath expr="." position="inside">
                <script type="text/javascript" src="/barcode_purchase_order/static/src/js/purchase.js"/>
            </xpath>
        </template>
    </data>
</openerp>