<s>
A	O
JavaScript	B-Language
engine	I-Language
is	O
a	O
software	O
component	O
that	O
executes	O
JavaScript	B-Language
code	O
.	O
</s>
<s>
The	O
first	O
JavaScript	B-Language
engines	I-Language
were	O
mere	O
interpreters	B-Application
,	O
but	O
all	O
relevant	O
modern	O
engines	B-Application
use	O
just-in-time	O
compilation	O
for	O
improved	O
performance	O
.	O
</s>
<s>
JavaScript	B-Language
engines	I-Language
are	O
typically	O
developed	O
by	O
web	B-Application
browser	I-Application
vendors	O
,	O
and	O
every	O
major	O
browser	B-Application
has	O
one	O
.	O
</s>
<s>
In	O
a	O
browser	B-Application
,	O
the	O
JavaScript	B-Language
engine	I-Language
runs	O
in	O
concert	O
with	O
the	O
rendering	B-Protocol
engine	I-Protocol
via	O
the	O
Document	B-General_Concept
Object	I-General_Concept
Model	I-General_Concept
.	O
</s>
<s>
The	O
use	O
of	O
JavaScript	B-Language
engines	I-Language
is	O
not	O
limited	O
to	O
browsers	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
the	O
V8	B-Language
engine	I-Language
is	O
a	O
core	O
component	O
of	O
the	O
Node.js	B-Language
and	O
Deno	B-Application
runtime	B-Device
systems	I-Device
.	O
</s>
<s>
Since	O
ECMAScript	B-Language
is	O
the	O
standardized	O
specification	O
of	O
JavaScript	B-Language
,	O
ECMAScript	B-Language
engine	I-Language
is	O
another	O
name	O
for	O
these	O
engines	B-Application
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
WebAssembly	B-Language
,	O
some	O
engines	B-Application
can	O
also	O
execute	O
this	O
code	O
in	O
the	O
same	O
sandbox	O
as	O
regular	O
JavaScript	B-Language
code	O
.	O
</s>
<s>
The	O
first	O
JavaScript	B-Language
engine	I-Language
was	O
created	O
by	O
Brendan	O
Eich	O
in	O
1995	O
for	O
the	O
Netscape	B-Protocol
Navigator	I-Protocol
web	B-Application
browser	I-Application
.	O
</s>
<s>
It	O
was	O
a	O
rudimentary	O
interpreter	B-Application
for	O
the	O
nascent	O
language	O
Eich	O
invented	O
.	O
</s>
<s>
(	O
This	O
evolved	O
into	O
the	O
SpiderMonkey	B-Language
engine	O
,	O
still	O
used	O
by	O
the	O
Firefox	B-Application
browser	I-Application
.	O
)	O
</s>
<s>
The	O
first	O
modern	O
JavaScript	B-Language
engine	I-Language
was	O
V8	B-Language
,	O
created	O
by	O
Google	B-Application
for	O
its	O
Chrome	B-Application
browser	I-Application
.	O
</s>
<s>
V8	B-Language
debuted	O
as	O
part	O
of	O
Chrome	B-Application
in	O
2008	O
,	O
and	O
its	O
performance	O
was	O
much	O
better	O
than	O
any	O
prior	O
engine	O
.	O
</s>
<s>
Other	O
browser	B-Application
vendors	O
needed	O
to	O
overhaul	O
their	O
interpreters	B-Application
to	O
compete	O
.	O
</s>
<s>
Apple	O
developed	O
the	O
Nitro	O
engine	O
for	O
its	O
Safari	B-Application
browser	I-Application
,	O
which	O
had	O
30%	O
better	O
performance	O
than	O
its	O
predecessor	O
.	O
</s>
<s>
Mozilla	B-Operating_System
leveraged	O
portions	O
of	O
Nitro	O
to	O
improve	O
its	O
own	O
SpiderMonkey	B-Language
engine	O
.	O
</s>
<s>
Since	O
2017	O
,	O
these	O
engines	B-Application
have	O
added	O
support	O
for	O
WebAssembly	B-Language
.	O
</s>
<s>
This	O
enables	O
the	O
use	O
of	O
pre-compiled	O
executables	B-Application
for	O
performance-critical	O
portions	O
of	O
page	O
scripts	O
.	O
</s>
<s>
V8	B-Language
from	O
Google	B-Application
is	O
the	O
most	O
used	O
JavaScript	B-Language
engine	I-Language
.	O
</s>
<s>
Google	B-Application
Chrome	I-Application
and	O
the	O
many	O
other	O
Chromium-based	O
browsers	B-Application
use	O
it	O
,	O
as	O
do	O
applications	B-Application
built	O
with	O
CEF	B-Language
,	O
Electron	B-Operating_System
,	O
or	O
any	O
other	O
framework	B-Architecture
that	O
embeds	O
Chromium	B-Language
.	O
</s>
<s>
Other	O
uses	O
include	O
the	O
Node.js	B-Language
and	O
Deno	B-Application
runtime	B-Device
systems	I-Device
.	O
</s>
<s>
SpiderMonkey	B-Language
is	O
developed	O
by	O
Mozilla	B-Operating_System
for	O
use	O
in	O
Firefox	B-Application
and	O
its	O
forks	B-Application
.	O
</s>
<s>
The	O
GNOME	B-Language
Shell	I-Language
uses	O
it	O
for	O
extension	O
support	O
.	O
</s>
<s>
JavaScriptCore	O
is	O
Apple	O
's	O
engine	O
for	O
its	O
Safari	B-Application
browser	I-Application
.	O
</s>
<s>
Other	O
WebKit-based	O
browsers	B-Application
also	O
use	O
it	O
.	O
</s>
<s>
KJS	B-Language
from	O
KDE	B-Application
was	O
the	O
starting	O
point	O
for	O
its	O
development	O
.	O
</s>
<s>
Chakra	B-Language
is	O
the	O
engine	O
of	O
the	O
Internet	B-Application
Explorer	I-Application
browser	B-Application
.	O
</s>
<s>
It	O
was	O
also	O
forked	O
by	O
Microsoft	O
for	O
the	O
original	O
Edge	B-Application
browser	I-Application
,	O
but	O
Edge	B-Application
was	O
later	O
rebuilt	O
as	O
a	O
Chromium-based	O
browser	B-Application
and	O
thus	O
now	O
uses	O
V8	B-Language
.	O
</s>
