<s>
Socket.IO	B-Language
is	O
an	O
event-driven	B-Application
library	O
for	O
real-time	O
web	B-Application
applications	I-Application
.	O
</s>
<s>
It	O
enables	O
real-time	O
,	O
bi-directional	O
communication	O
between	O
web	B-Application
clients	I-Application
and	O
servers	O
.	O
</s>
<s>
It	O
consists	O
of	O
two	O
parts	O
:	O
a	O
client-side	B-Operating_System
library	O
that	O
runs	O
in	O
the	O
browser	B-Application
,	O
and	O
a	O
server-side	B-Application
library	O
for	O
Node.js	B-Language
.	O
</s>
<s>
Both	O
components	O
have	O
a	O
nearly	O
identical	O
API	B-Application
.	O
</s>
<s>
Socket.IO	B-Language
primarily	O
uses	O
the	O
WebSocket	B-Protocol
protocol	O
with	O
polling	O
as	O
a	O
fallback	O
option	O
,	O
while	O
providing	O
the	O
same	O
interface	O
.	O
</s>
<s>
Although	O
it	O
can	O
be	O
used	O
simply	O
as	O
a	O
wrapper	B-Library
for	O
WebSockets	B-Protocol
,	O
it	O
provides	O
many	O
more	O
features	O
,	O
including	O
broadcasting	O
to	O
multiple	O
sockets	O
,	O
storing	O
data	O
associated	O
with	O
each	O
client	O
,	O
and	O
asynchronous	B-Architecture
I/O	I-Architecture
.	O
</s>
<s>
It	O
can	O
be	O
installed	O
with	O
the	O
Node	B-Language
Package	I-Language
Manager	I-Language
(	O
NPM	B-Language
)	O
.	O
</s>
<s>
Socket.IO	B-Language
provides	O
the	O
ability	O
to	O
implement	O
real-time	O
analytics	O
,	O
binary	O
streaming	O
,	O
instant	B-Application
messaging	I-Application
,	O
and	O
document	O
collaboration	O
.	O
</s>
<s>
Notable	O
users	O
include	O
Microsoft	B-Application
Office	I-Application
,	O
Yammer	B-Protocol
and	O
Zendesk	O
.	O
</s>
<s>
Socket.IO	B-Language
handles	O
the	O
connection	O
transparently	O
and	O
will	O
automatically	O
upgrade	O
to	O
WebSocket	B-Protocol
if	O
possible	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
developer	O
does	O
not	O
need	O
to	O
know	O
how	O
to	O
use	O
the	O
WebSocket	B-Protocol
protocol	O
in	O
order	O
to	O
use	O
Socket.IO	B-Language
.	O
</s>
<s>
Socket.IO	B-Language
is	O
not	O
a	O
WebSocket	B-Protocol
library	O
with	O
fallback	O
options	O
to	O
other	O
real-time	O
protocols	O
.	O
</s>
<s>
A	O
Socket.IO	B-Language
implementing	O
server	O
cannot	O
connect	O
to	O
a	O
non-Socket.IO	O
WebSocket	B-Protocol
client	O
.	O
</s>
<s>
A	O
Socket.IO	B-Language
implementing	O
client	O
cannot	O
talk	O
to	O
a	O
non-Socket.IO	O
WebSocket	B-Protocol
or	O
Long	O
Polling	O
Comet	B-General_Concept
server	O
.	O
</s>
<s>
Socket.IO	B-Language
requires	O
using	O
the	O
Socket.IO	B-Language
libraries	O
on	O
both	O
client	O
and	O
server	B-Application
side	I-Application
.	O
</s>
<s>
As	O
of	O
version	O
2.0	O
,	O
Socket.IO	B-Language
makes	O
use	O
of	O
WebSockets	B-Protocol
as	O
the	O
underlying	O
WebSocket	B-Protocol
library	O
.	O
</s>
