var purchaseOrder=nlapiCreateRecord('purchaseorder', {recordmode: 'dynamic'});
purchaseOrder.setFieldValue('entity', 38);
purchaseOrder.selectNewLineItem('item');
purchaseOrder.setCurrentLineItemValue('item', 'item', 909 );
purchaseOrder.setCurrentLineItemValue('item', 'quantity', 1);
var invDetailSubrecord = purchaseOrder.createCurrentLineItemSubrecord('item', 'inventorydetail');
invDetailSubrecord.selectNewLineItem('inventoryassignment');
invDetailSubrecord.setCurrentLineItemValue('inventoryassignment', 'receiptinventorynumber', 'EIOJNF98');