<s>
ECMAScript	B-Language
(	O
;	O
ES	O
)	O
is	O
a	O
JavaScript	B-Language
standard	O
intended	O
to	O
ensure	O
the	O
interoperability	O
of	O
web	O
pages	O
across	O
different	O
browsers	B-Application
.	O
</s>
<s>
ECMAScript	B-Language
is	O
commonly	O
used	O
for	O
client-side	O
scripting	O
on	O
the	O
World	O
Wide	O
Web	O
,	O
and	O
it	O
is	O
increasingly	O
being	O
used	O
for	O
writing	O
server-side	O
applications	O
and	O
services	O
using	O
Node.js	B-Language
and	O
other	O
runtime	O
environments	O
.	O
</s>
<s>
ECMA-262	B-Language
,	O
or	O
the	O
ECMAScript	B-Language
Language	O
Specification	O
,	O
defines	O
the	O
ECMAScript	B-Language
Language	O
,	O
or	O
just	O
ECMAScript	B-Language
.	O
</s>
<s>
ECMA-262	B-Language
specifies	O
only	O
language	O
syntax	O
and	O
the	O
semantics	O
of	O
the	O
core	O
API	B-General_Concept
,	O
such	O
as	O
,	O
,	O
and	O
,	O
while	O
valid	O
implementations	O
of	O
JavaScript	B-Language
add	O
their	O
own	O
functionality	O
such	O
as	O
input-output	O
and	O
file-system	O
handling	O
.	O
</s>
<s>
The	O
ECMAScript	B-Language
specification	O
is	O
a	O
standardized	O
specification	O
of	O
a	O
scripting	B-Language
language	I-Language
developed	O
by	O
Brendan	O
Eich	O
of	O
Netscape	O
;	O
initially	O
named	O
Mocha	B-Language
,	O
then	O
LiveScript	O
,	O
and	O
finally	O
JavaScript	B-Language
.	O
</s>
<s>
In	O
December	O
1995	O
,	O
Sun	O
Microsystems	O
and	O
Netscape	O
announced	O
JavaScript	B-Language
in	O
a	O
press	O
release	O
.	O
</s>
<s>
In	O
November	O
1996	O
,	O
Netscape	O
announced	O
a	O
meeting	O
of	O
the	O
Ecma	O
International	O
standards	O
organization	O
to	O
advance	O
the	O
standardization	O
of	O
JavaScript	B-Language
.	O
</s>
<s>
The	O
first	O
edition	O
of	O
ECMA-262	B-Language
was	O
adopted	O
by	O
the	O
Ecma	O
General	O
Assembly	O
in	O
June	O
1997	O
.	O
</s>
<s>
The	O
name	O
"	O
ECMAScript	B-Language
"	O
was	O
a	O
compromise	O
between	O
the	O
organizations	O
involved	O
in	O
standardizing	O
the	O
language	O
,	O
especially	O
Netscape	O
and	O
Microsoft	O
,	O
whose	O
disputes	O
dominated	O
the	O
early	O
standards	O
sessions	O
.	O
</s>
<s>
Eich	O
commented	O
that	O
"	O
ECMAScript	B-Language
was	O
always	O
an	O
unwanted	O
trade	O
name	O
that	O
sounds	O
like	O
a	O
skin	O
disease.	O
"	O
</s>
<s>
ECMAScript	B-Language
has	O
been	O
formalized	O
through	O
operational	O
semantics	O
by	O
work	O
at	O
Stanford	O
University	O
and	O
the	O
Department	O
of	O
Computing	O
,	O
Imperial	O
College	O
London	O
for	O
security	O
analysis	O
and	O
standardization	O
.	O
</s>
<s>
The	O
ECMAScript	B-Language
language	O
includes	O
structured	B-Language
,	O
dynamic	B-Language
,	O
functional	B-Language
,	O
and	O
prototype-based	B-Application
features	O
.	O
</s>
<s>
ECMAScript	B-Language
JavaScript	B-Language
supports	O
C	B-Language
style	O
structured	B-Language
programming	I-Language
.	O
</s>
<s>
Previously	O
,	O
JavaScript	B-Language
only	O
supported	O
function	B-Language
scoping	I-Language
using	O
the	O
keyword	O
var	O
,	O
but	O
ECMAScript	B-Language
2015	O
added	O
the	O
keywords	O
let	O
and	O
const	O
allowing	O
JavaScript	B-Language
to	O
support	O
both	O
block	O
scoping	B-Language
and	O
function	B-Language
scoping	I-Language
.	O
</s>
<s>
JavaScript	B-Language
supports	O
automatic	O
semicolon	O
insertion	O
,	O
meaning	O
that	O
semicolons	O
that	O
are	O
normally	O
used	O
to	O
terminate	O
a	O
statement	O
in	O
C	B-Language
may	O
be	O
omitted	O
in	O
JavaScript	B-Language
.	O
</s>
<s>
Like	O
C-style	O
languages	O
,	O
control	O
flow	O
is	O
done	O
with	O
the	O
,	O
,	O
/	O
,	O
/	O
,	O
and	O
statements	O
.	O
</s>
<s>
ECMAScript	B-Language
is	O
weakly	O
typed	O
.	O
</s>
<s>
However	O
,	O
there	O
are	O
several	O
quirks	O
in	O
JavaScript	B-Language
's	O
implementation	O
of	O
the	O
conversion	O
of	O
a	O
variable	O
from	O
one	O
type	O
to	O
another	O
.	O
</s>
<s>
ECMAScript	B-Language
is	O
dynamically	O
typed	O
.	O
</s>
<s>
ECMAScript	B-Language
supports	O
various	O
ways	O
to	O
test	O
the	O
type	O
of	O
objects	O
,	O
including	O
duck	B-Application
typing	I-Application
.	O
</s>
<s>
Since	O
ES	O
2015	O
,	O
transpiling	B-Language
JavaScript	B-Language
has	O
become	O
very	O
common	O
.	O
</s>
<s>
Transpilation	B-Language
is	O
a	O
source-to-source	B-Language
compilation	I-Language
in	O
which	O
newer	O
versions	O
of	O
JavaScript	B-Language
are	O
used	O
,	O
and	O
a	O
transpiler	B-Language
rewrites	O
the	O
source	O
code	O
so	O
that	O
it	O
is	O
supported	O
by	O
older	O
browsers	B-Application
.	O
</s>
<s>
Usually	O
,	O
transpilers	B-Language
transpile	B-Language
down	O
to	O
ES3	O
to	O
maintain	O
compatibility	O
with	O
all	O
versions	O
of	O
browsers	B-Application
.	O
</s>
<s>
The	O
settings	O
to	O
transpiling	B-Language
to	O
a	O
specific	O
version	O
can	O
be	O
configured	O
according	O
to	O
need	O
.	O
</s>
<s>
Transpiling	B-Language
adds	O
an	O
extra	O
step	O
to	O
the	O
build	O
process	O
and	O
is	O
sometimes	O
done	O
to	O
avoid	O
needing	O
polyfills	B-Protocol
.	O
</s>
<s>
Polyfills	B-Protocol
create	O
new	O
features	O
for	O
older	O
environments	O
that	O
lack	O
them	O
.	O
</s>
<s>
Polyfills	B-Protocol
do	O
this	O
at	O
runtime	O
in	O
the	O
interpreter	O
,	O
such	O
as	O
the	O
user	O
's	O
browser	B-Application
or	O
on	O
the	O
server	O
.	O
</s>
<s>
Instead	O
,	O
transpiling	B-Language
rewrites	O
the	O
ECMA	O
code	O
itself	O
during	O
the	O
build	O
phase	O
of	O
development	O
before	O
it	O
reaches	O
the	O
interpreter	O
.	O
</s>
<s>
In	O
2010	O
,	O
Ecma	O
International	O
started	O
developing	O
a	O
standards	O
test	O
for	O
Ecma	B-Language
262	I-Language
ECMAScript	B-Language
.	O
</s>
<s>
Test262	O
is	O
an	O
ECMAScript	B-Language
conformance	O
test	O
suite	O
that	O
can	O
be	O
used	O
to	O
check	O
how	O
closely	O
a	O
JavaScript	B-Language
implementation	O
follows	O
the	O
ECMAScript	B-Language
Specification	O
.	O
</s>
<s>
The	O
test	O
suite	O
contains	O
thousands	O
of	O
individual	O
tests	O
,	O
each	O
of	O
which	O
tests	O
some	O
specific	O
requirement(s )	O
of	O
the	O
ECMAScript	B-Language
specification	O
.	O
</s>
<s>
ECMAScript	B-Language
specifications	O
through	O
ES7	O
are	O
well-supported	O
in	O
major	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
The	O
table	O
below	O
shows	O
the	O
conformance	O
rate	O
for	O
current	O
versions	O
of	O
software	O
with	O
respect	O
to	O
the	O
most	O
recent	O
editions	O
of	O
ECMAScript	B-Language
.	O
</s>
<s>
+Scripting	O
engine	O
conformance	O
Scripting	B-Language
engine	I-Language
Reference	O
application(s )	O
ConformanceES5	O
is	O
the	O
baseline	O
for	O
this	O
test	O
suite	O
.	O
</s>
