pos/pos_backend_partner/static/src/js/back_partner.js

'use strict';
odoo.define('pos_backend_partner.partner_back', function (require) {
    var translation = require('web.translation');
    var _t = translation._t;

    var tools = require('pos_backend_communication.back');

    if (tools.is_tied_to_pos()) {
        tools.callbacks['partner.choose'] = function() {
            //get focus with alert
            //TODO: replace with notifications
            alert(_t('Choose a customer'));
        };
        //tell the POS we are ready to receive
        tools.sendMessage({type: 'partner.ready'});
    }
});