JavaScript Reserved Words

In JavaScript you cannot use these reserved words as variables, labels, or function names:

abstract	arguments	await*	boolean
break	byte	case	catch
char	class*	const	continue
debugger	default	delete	do
double	else	enum*	eval
export*	extends*	false	final
finally	float	for	function
goto	if	implements	import*
in	instanceof	int	interface
let*	long	native	new
null	package	private	protected
public	return	short	static
super*	switch	synchronized	this
throw	throws	transient	true
try	typeof	var	void
volatile	while	with	yield

Words marked with* are new in ECMAScript 5 and 6.

You can read more about the different JavaScript versions in the chapter JS Versions.

Removed Reserved Words

The following reserved words have been removed from the ECMAScript 5/6 standard:

abstract	boolean	byte	char
double	final	float	goto
int	long	native	short
synchronized	throws	transient	volatile

Do not use these words as variables. ECMAScript 5/6 does not have full support in all browsers.

JavaScript Objects, Properties, and Methods

You should also avoid using the name of JavaScript built-in objects, properties, and methods:

Array	Date	eval	function
hasOwnProperty	Infinity	isFinite	isNaN
isPrototypeOf	length	Math	NaN
name	Number	Object	prototype
String	toString	undefined	valueOf

Java Reserved Words

JavaScript is often used together with Java. You should avoid using some Java objects and properties as JavaScript identifiers:

getClass	java	JavaArray	javaClass
JavaObject	JavaPackage

Other Reserved Words

JavaScript can be used as the programming language in many applications.You should also avoid using the name of HTML and Window objects and properties:

alert	all	anchor	anchors
area	assign	blur	button
checkbox	clearInterval	clearTimeout	clientInformation
close	closed	confirm	constructor
crypto	decodeURI	decodeURIComponent	defaultStatus
document	element	elements	embed
embeds	encodeURI	encodeURIComponent	escape
event	fileUpload	focus	form
forms	frame	innerHeight	innerWidth
layer	layers	link	location
mimeTypes	navigate	navigator	frames
frameRate	hidden	history	image
images	offscreenBuffering	open	opener
option	outerHeight	outerWidth	packages
pageXOffset	pageYOffset	parent	parseFloat
parseInt	password	pkcs11	plugin
prompt	propertyIsEnum	radio	reset
screenX	screenY	scroll	secure
select	self	setInterval	setTimeout
status	submit	taint	text
textarea	top	unescape	untaint
window

HTML Event Handlers

In addition you should avoid using the name of all HTML event handlers.Examples:

onblur	onclick	onerror	onfocus
onkeydown	onkeypress	onkeyup	onmouseover
onload	onmouseup	onmousedown	onsubmit