In an array of JSON objects, access first json object from within the second json object in the array

Question

frappe.query_reports["Script Report"] = {
    filters: [
        {
            fieldname:"purchase_order",
            label: __("Purchase Order"),
            fieldtype: "Link",
            options: "Purchase Order",
        },
        
        {
            fieldname:"purchaseorder",
            label: __("PurchaseOrder"),
            fieldtype: "Select",
            options: function(x),
        },
        
    ],
};

I am making a script report in ERPNext, where I have to use the first Filter's value and show an list of options in the second filter for the user to select. How can I refer to fieldname of the first JSON Oject in place of x in function(x)?

I searched erpnext and frappe documentation but couldn't find anything. I assume it is a javascript problem I am facing.