Reserved Word

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ECMAScript edition - 2

Reserved words are keywords that the interpreter uses to determine the instructions your script is going to execute.

Generally, reserved words will be one of the following:

A keyword
A reserved word
A null literal
A Boolean literal

Here is a complete list of reserved words as defined by the ECMA 262 standard. It also includes words that are dangerous because they are properties or method names.

Name	Notes
abstract	Java keyword reserved
alert	Identifier name
arguments	Identifier name
Array	Object type
blur	Identifier name
boolean	Java keyword reserved
Boolean	Object type
break	Keyword
byte	Java keyword reserved
callee	Identifier name
caller	Identifier name
captureEvents	Identifier name
case	Keyword
catch	Reserved word
char	Java keyword reserved
class	Reserved word
clearInterval	Identifier name
clearTimeout	Identifier name
close	Identifier name
closed	Identifier name
confirm	Identifier name
const	Reserved word
constructor	Identifier name
continue	Keyword
Date	Object type
debugger	Reserved word
default	Keyword
defaultStatus	Identifier name
delete	Keyword
do	Keyword
document	Identifier name
double	Java keyword reserved
else	Keyword
enum	Reserved word
escape	Identifier name
eval	Identifier name
export	Keyword
extends	Reserved word
false	Boolean literal
final	Java keyword reserved
finally	Keyword
find	Identifier name
float	Java keyword reserved
focus	Identifier name
for	Keyword
frames	Identifier name
function	Keyword
Function	Object type
goto	Java keyword reserved
history	Identifier name
home	Identifier name
if	Keyword
implements	Java keyword reserved
import	Keyword
in	Keyword
Infinity	Global special variable
innerHeight	Identifier name
innerWidth	Identifier name
instanceof	Keyword
int	Java keyword reserved
interface	Java keyword reserved
isFinite	Identifier name
isNaN	Identifier name
java	Identifier name
length	Identifier name
location	Identifier name
locationbar	Identifier name
long	Java keyword reserved
Math	Object type
menubar	Identifier name
moveBy	Identifier name
moveTo	Identifier name
name	Identifier name
NaN	Global special variable
native	Java keyword reserved
netscape	Identifier name
new	Keyword
null	Null literal
Number	Object type
Object	Object type
open	Identifier name
opener	Identifier name
outerHeight	Identifier name
outerWidth	Identifier name
package	Java keyword reserved
Packages	Identifier name
pageXOffset	Identifier name
pageYOffset	Identifier name
parent	Identifier name
parseFloat	Identifier name
parseInt	Identifier name
personalbar	Identifier name
print	Identifier name
private	Java keyword reserved
prompt	Identifier name
protected	Java keyword reserved
prototype	Identifier name
public	Java keyword reserved
RegExp	Identifier name
releaseEvents	Identifier name
resizeBy	Identifier name
resizeTo	Identifier name
return	Keyword
routeEvent	Identifier name
scroll	Identifier name
scrollbars	Identifier name
scrollBy	Identifier name
scrollTo	Identifier name
self	Identifier name
setInterval	Identifier name
setTimeout	Identifier name
short	Java keyword reserved
static	Java keyword reserved
status	Identifier name
statusbar	Identifier name
stop	Identifier name
String	Object type
super	Reserved word
switch	Keyword
synchronized	Java keyword reserved
this	Keyword
throw	Keyword
throws	Java keyword reserved
toolbar	Identifier name
top	Identifier name
toString	Identifier name
transient	Java keyword reserved
true	Boolean literal
try	Keyword
typeof	Keyword
unescape	Identifier name
unwatch	Identifier name
valueOf	Identifier name
var	Keyword
void	Keyword
volatile	Reserved word
watch	Identifier name
while	Keyword
window	Identifier name
with	Keyword

Looking at the some of the particular keywords being reserved, it suggests that future revisions of ECMAScript will become more object oriented. Or at least even if the underlying implementation is not truly object oriented, then the visible interface to the interpreter from a script will behave very much as if it is.

The third edition of the ECMA standard does not add any new keywords but removes those that have been defined as part of the upgrade to the standard. There are still several that are classed as reserved words that have already been implemented in some browser versions. Simply avoiding parse errors does not qualify them as features to be documented as being available in the browser.

On the Netscape developer web site, there is talk of developing a version 2.0 of the JavaScript language, to change JavaScript into a truly class-based object oriented language. At that time, many of the currently reserved words will likely become functional parts of the language.

Warnings:

You must not use reserved words as identifier names.
The table lists words you should avoid in a client-side context. You could argue that because alert is not a reserved word on the server-side that it would be safe to use it there. I would recommend against that because it is possible you might develop a library of JavaScript functions for general purpose use. It wouldn't be hard to imagine how an identifier that was server-side safe could eventually end up being executed client-side.
The list in the table is not exhaustive and you should always think carefully about the identifier names you choose for properties, methods, functions, and variables.

Cross-references:

ECMA 262 edition 2 - section - 7.4.1

ECMA 262 edition 3 - section - 7.5.1

O'Reilly JavaScript Definitive Guide - page - 31

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Reserved Word (Definition)

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