var pdfs = [];

// later on inside a loop...
var pdf = render.transaction({entityId: results[i]['id']});

// still later
var archiver = compress.createArchiver();
				
for(var i = 0; i < pdfs.length; i++) {				
					
	archiver.add({file: pdfs[i]});

}

// and then 
var filename = context.request.parameters.filename;
				
// If it doesn't end in .zip add that in.
if(!filename.endsWith('/.zip'))
filename += '.zip';
				
var zip = archiver.archive({name: filename});	
								
context.response.writeFile({file: zip});