SPservices get listitemid

Question

I'm following this example on how to get the links to list attachments. My console logs 'ReferenceError: id is not defined'. If I, however, hard code an arbitrary listitemid (i.e. 1), the code works fine. My code is as follows:

$().SPServices({
    operation: "GetAttachmentCollection",
    listName: "mylist", //my list name
    ID: id,

    completefunc: function(xData, Status) {
        //console.log( Status );
        //console.log( xData.responseText );

        var output = "";

        //debugger;

        $(xData.responseXML).find("Attachments > Attachment").each(function(i, el) {
            var $node = $(this),
            filePath = $node.text(),
            arrString = filePath.split("/"),
            fileName = arrString[arrString.length - 1];

          output += "<a href='" + filePath + "' target='_blank'>" + fileName + "</a><br />";
        });

        $("#drop-zone").html(output);
    }
});    

ID seems to be set incorrectly (should refer to the listitemid). I have no idea on how to retrieve the correct id of a list. Can someone explain to me how I can obtain the listitemid of the item I'm currently creating? The code is added to the newifs.aspx of a certain list - if that matters - .