JavaScript Reserved Words

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

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

abstract	arguments	async *	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
function	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
using *	var	void	volatile
while	with	yield *

Words marked with* have been added to JavaScript from after 2015. > You can read more the newest JavaScript versions in JS News 2025-2015.

Removed Reserved Words

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

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

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

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

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

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