saas-platform/frontend/saas-web/app/view/purchase/order/FormModel.js

Ext.define('saas.view.purchase.order.FormModel', {
    extend: 'Ext.app.ViewModel',
    alias: 'viewmodel.purchase-order-formmodel',

    data: {
        id: 'TC-1032301'
    },

    formulas: {
        sum: function(get) {
            return get('num1') + get('num2');
        }
    }
});