<s>
Underscore.js	B-Language
is	O
a	O
JavaScript	B-Language
library	I-Language
which	O
provides	O
utility	O
functions	O
for	O
common	O
programming	O
tasks	O
.	O
</s>
<s>
It	O
is	O
comparable	O
to	O
features	O
provided	O
by	O
Prototype.js	B-Language
and	O
the	O
Ruby	B-Language
language	I-Language
,	O
but	O
opts	O
for	O
a	O
functional	B-Language
programming	I-Language
design	O
instead	O
of	O
extending	O
object	O
prototypes	B-Application
.	O
</s>
<s>
The	O
documentation	O
refers	O
to	O
Underscore.js	B-Language
as	O
"	O
the	O
tie	O
to	O
go	O
along	O
with	O
jQuery	B-Language
's	O
tux	O
,	O
and	O
Backbone.js	B-Language
'	O
suspenders.	O
"	O
</s>
<s>
Underscore.js	B-Language
was	O
created	O
by	O
Jeremy	O
Ashkenas	O
,	O
who	O
is	O
also	O
known	O
for	O
Backbone.js	B-Language
and	O
CoffeeScript	B-Application
.	O
</s>
<s>
Jeremy	O
Ashkenas	O
created	O
Underscore	O
by	O
the	O
end	O
of	O
2009	O
as	O
a	O
spin-off	O
from	O
the	O
DocumentCloud	O
project	O
,	O
together	O
with	O
Backbone.js	B-Language
.	O
</s>
<s>
It	O
was	O
one	O
of	O
the	O
earliest	O
libraries	O
for	O
JavaScript	B-Language
to	O
provide	O
general	O
functional	B-Language
programming	I-Language
utilities	O
,	O
taking	O
inspiration	O
from	O
Prototype.js	B-Language
,	O
Oliver	O
Steele	O
's	O
Functional	O
JavaScript	B-Language
,	O
and	O
John	O
Resig	O
's	O
Micro-Templating	O
.	O
</s>
<s>
In	O
2012	O
,	O
John-David	O
Dalton	O
created	O
a	O
fork	B-Application
of	O
Underscore	O
,	O
named	O
Lo-Dash	O
(	O
now	O
Lodash	B-Language
)	O
.	O
</s>
<s>
Nevertheless	O
,	O
Lodash	B-Language
already	O
departed	O
from	O
the	O
original	O
Underscore	O
interface	O
at	O
an	O
early	O
stage	O
and	O
started	O
making	O
more	O
drastic	O
changes	O
with	O
the	O
3.0.0	O
release	O
,	O
making	O
it	O
necessary	O
for	O
Lodash	B-Language
users	O
to	O
change	O
their	O
code	O
.	O
</s>
<s>
Despite	O
concerns	O
about	O
code	O
style	O
and	O
code	O
size	O
,	O
Ashkenas	O
was	O
not	O
opposed	O
to	O
merging	O
some	O
of	O
Lodash	B-Language
's	O
extensions	O
into	O
Underscore	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
there	O
were	O
several	O
developers	O
contributing	O
to	O
Underscore	O
and	O
Lodash	B-Language
in	O
parallel	O
;	O
this	O
group	O
of	O
contributors	O
started	O
making	O
changes	O
to	O
Underscore	O
in	O
order	O
to	O
make	O
it	O
more	O
like	O
Lodash	B-Language
.	O
</s>
<s>
In	O
parallel	O
to	O
this	O
effort	O
,	O
however	O
,	O
Dalton	O
made	O
more	O
drastic	O
changes	O
to	O
the	O
Lodash	B-Language
interface	O
.	O
</s>
<s>
In	O
June	O
2015	O
,	O
he	O
announced	O
Lodash	B-Language
version	O
4.0.0	O
,	O
which	O
distanced	O
Lodash	B-Language
even	O
further	O
from	O
the	O
Underscore	O
interface	O
,	O
while	O
making	O
a	O
significant	O
departure	O
from	O
the	O
version	O
3.x	O
series	O
of	O
Lodash	B-Language
itself	O
as	O
well	O
.	O
</s>
<s>
This	O
prompted	O
some	O
projects	O
that	O
depended	O
on	O
Lodash	B-Language
to	O
create	O
their	O
own	O
distributions	O
of	O
Lodash	B-Language
3	O
.	O
</s>
<s>
He	O
suggested	O
that	O
users	O
switch	O
from	O
Underscore	O
to	O
Lodash	B-Language
,	O
motivating	O
this	O
with	O
usage	O
share	O
statistics	O
.	O
</s>
<s>
Over	O
time	O
,	O
newer	O
versions	O
of	O
the	O
ECMAScript	B-Language
standard	O
have	O
added	O
built-in	O
functions	O
to	O
the	O
language	O
that	O
replicate	O
some	O
of	O
the	O
functionality	O
of	O
Underscore	O
,	O
such	O
as	O
Object.assign	O
and	O
Array.prototype.map	O
.	O
</s>
<s>
This	O
may	O
lead	O
to	O
the	O
perception	O
that	O
Underscore	O
no	O
longer	O
adds	O
value	O
to	O
a	O
JavaScript	B-Language
project	O
,	O
although	O
the	O
built-in	O
functions	O
are	O
however	O
less	O
powerful	O
than	O
their	O
Underscore	O
equivalents	O
;	O
in	O
particular	O
,	O
built-in	O
array	O
iteration	O
methods	O
such	O
as	O
map	O
,	O
filter	O
and	O
forEach	O
cannot	O
iterate	O
over	O
plain	O
objects	O
and	O
do	O
not	O
support	O
iteratee	O
shorthands	O
.	O
</s>
<s>
The	O
library	O
is	O
still	O
widely	O
depended	O
upon	O
and	O
is	O
being	O
downloaded	O
from	O
npm	B-Language
several	O
million	O
times	O
every	O
week	O
.	O
</s>
<s>
Function	B-Language
functions	I-Language
such	O
as	O
bind	O
,	O
memoize	O
,	O
partial	O
and	O
debounce	O
take	O
a	O
function	O
as	O
argument	O
and	O
return	O
a	O
new	O
function	O
with	O
altered	O
properties	O
(	O
higher-order	B-Language
functions	I-Language
)	O
.	O
</s>
<s>
Literate	B-Application
source	O
code	O
that	O
is	O
meant	O
to	O
be	O
read	O
,	O
so	O
that	O
it	O
is	O
easy	O
to	O
follow	O
how	O
the	O
library	O
is	O
implemented	O
.	O
</s>
<s>
Since	O
version	O
1.11	O
,	O
Underscore	O
is	O
modular	B-Architecture
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
the	O
documentation	O
now	O
includes	O
both	O
a	O
of	O
the	O
annotated	O
source	O
,	O
in	O
which	O
each	O
function	O
is	O
on	O
a	O
separate	O
page	O
and	O
the	O
import	O
references	O
are	O
clickable	O
hyperlinks	O
,	O
and	O
a	O
,	O
where	O
all	O
functions	O
are	O
on	O
a	O
single	O
page	O
by	O
order	B-Algorithm
of	I-Algorithm
dependency	I-Algorithm
.	O
</s>
<s>
Underscore	O
promotes	O
a	O
functional	B-Language
style	I-Language
,	O
where	O
multiple	O
functions	O
can	O
be	O
combined	O
in	O
a	O
single	O
expression	O
in	O
order	O
to	O
obtain	O
new	O
functionality	O
.	O
</s>
<s>
partial	O
creates	O
a	O
partially	B-Application
applied	I-Application
version	O
of	O
a	O
function	O
and	O
_	O
can	O
be	O
used	O
to	O
leave	O
some	O
parameters	O
"	O
open	O
"	O
so	O
that	O
these	O
can	O
be	O
supplied	O
later	O
.	O
</s>
<s>
With	O
the	O
arrival	O
of	O
modules	B-Architecture
in	O
ES6	O
,	O
having	O
such	O
a	O
namespace	O
handle	O
is	O
no	O
longer	O
strictly	O
necessary	O
,	O
but	O
the	O
practice	O
is	O
still	O
commonly	O
found	O
in	O
code	O
using	O
older	O
module	B-Architecture
systems	I-Architecture
such	O
as	O
AMD	B-Language
and	O
CommonJS	B-Language
:	O
</s>
