times called a verb) and a URL path. You might be surprised to see two requests each
time you go to that URL in the browser:
GET /
GET /favicon.ico
Most browsers will request an icon that they can display in the URL bar or tab; the
browser will do this implicitly, which is why we see it logged on the console.
At the heart of Node’s web server is the callback function that you provide, that will
respond to all incoming requests. It takes two arguments, an
IncomingMessage
object
(often abbreviated
req
) and a
ServerRequest
object (often abbreviated
res
). The
IncomingMessage
object contains all information about the HTTP request: what URL
was requested, any headers that were sent, any data sent in the body, and more. The
ServerResponse
object contains properties and methods to control the response that
will be sent back to the client (usually a browser). If you saw that we called
req.end
and wondered if
req
is a write stream, go to the head of the class. The
ServerRes
ponse
object implements the writable stream interface, which is how you write data
to the client. Because the
ServerResponse
object is a write stream, it makes it easy to
send a file…we can just create a file read stream and pipe it to the HTTP response.
For example, if you have a favicon.ico file to make your website look nicer, you could
detect this request and send this file directly:
const
server
=
http
.
createServer
(
function
(
req
,
res
) {
if
(
req
.
method
===
'GET'
&&
req
.
url
===
'/favicon.ico'
) {
const
fs
=
require
(
'fs'
);
fs
.
createReadStream
(
'favicon.ico'
);
fs
.
pipe
(
res
);
// this replaces the call to 'end'
}
else
{
console.log(
`
${
req
.
method
}
${
req
.
url
}
`
);
res
.
end
(
'Hello world!'
);
}
});
This a minimal web server, though not a very interesting one. With the information
contained in
IncomingRequest
, you can expand this model to create any kind of web‐
site you wish.
If you’re using Node to serve websites, you’ll probably want to look into using a
framework such as
that will take some of the drudgery out of building
a web server from scratch.
Koa is something of a successor to the very popular Express, and
it’s no coincidence: both are the work of TJ Holowaychuk. If you’re
already familiar with Express, you will feel right at home with Koa
—except that you get to enjoy a more ES6-centric approach to web
development.
298 | Chapter 20: Node
