sending-responses.md

Sending responses

The route handler usually needs to call a method on the response object to send back some responses.

Here are a few common ways to send back responses:

Method	Description
res.status(yourResponseStatusCode)	Send HTTP status response code (e.g. 200, 404, etc)
res.json(yourResponse)	Send a JSON response.
res.send(yourResponse)	Send a response of various formats (e.g. plain text, html, etc)

Example: Setting status code in response

res.status(200).send("OK");

That is the same as

res.sendStatus(200);

Example: Send back a JSON in response body

res.set("Content-Type", "application/json").send({ name: "Jon", age: 30 });

The same thing can we written as

res.json({ name: "Jon", age: 30 });

Example: Send back a JSON in response when error happens

res.status(500).json({ error: "some unexpected error" });

Reference

Here are some other ways to send back responses. Find out their details on Express Framework documentation

Method	Description
res.write()	Write some data to the response buffer, but don't send it until you call res.end()
res.end()	End the response process.
res.redirect()	Redirect a request.
res.download()	Prompt a file to be downloaded.
res.jsonp()	Send a JSON response with JSONP support.
res.render()	Render a view template.
res.sendFile()	Send a file as attachment in response.

What's the difference between res.send() and res.write() API?

The major difference is the send() API automatically set Content-Type in response header. That's handy sometimes, but if you call send() API multiple times, you will get error like "Can't set headers after they are sent."

To avoid that issue, you can set Content-Type response header by yourself, call res.write() multiple times, and call res.end() at last.

A more detailed comparison can be found here and here