There are a number of words that make up the components of the JavaScript language. Thes words cannot be used for variable or funciotn names because the program interpreter would be unable to distinguish between a default javascript command and your variable or function name.

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