Express 4.x uses res.set instead of res.setHeader

[shane-tomlinson]

See http://expressjs.com/api.html#res.set

[elf-pavlik]

also

'app.router' is deprecated!

while examples in README use it

[troygoode]

thanks for the heads up @shane-tomlinson and @elf-pavlik

[markstos]

Express 4 inherits in the HTTP ServerResponse prototype:

var res = Object.create(http.ServerResponse.prototype)

Which means that all the methods available on HTTP ServerResponse class are available on the Express response object. This includes the setHeader method:

https://nodejs.org/api/http.html#http_response_removeheader_name

This is documented in the opening stanza of the Express "Response" object:

The res object is an enhanced version of Node’s own response object and supports all built-in fields and methods.

And it links to the docs for the "HTTP ServerResponse" class from there.

So, both res.setHeader() and res.set() officially work in Express 4.

res.setHeader() will perform slightly better, since res.set() is just a wrapper which calls res.setHeader().