Node.js response API vs. Express.js response API

Both, Node.js and Express.js have response API. And it looks like there is even some overlapping between them, e.g.: Node.js: response.write(chunk[, encoding][, callback]) Express.js: res.attachment([filename]) res.download(path [, filename] [, options] [, fn]) res.sendFile(path [, options] [, fn]) res.send([body]) Which response API should be used for sending a response (e.g. JSON, files)? In other words, should I use response.write by Node.js or res.sendFile by Express.js? P.S. Initially for some reason I assumed that Express.js is now a part of Node.js, which is not a right assumption, of course. Answer Bearing in mind that Express.js is now a part of Node.js It