JavaScript: The Definitive Guide, Fourth Edition

Reserved Words

There are a number of reserved words in JavaScript. These are words that you cannot use as identifiers (variable names, function names, and loop labels) in your JavaScript programs. Table 2-1 lists the keywords standardized by ECMAScript v3. These words have special meaning to JavaScript -- they are part of the language syntax itself.

Table 2-1. Reserved JavaScript keywords

break	do	if	switch	typeof
case	else	in	this	var
catch	false	instanceof	throw	void
continue	finally	new	true	while
default	for	null	try	with
delete	function	return

Table 2-2 lists other reserved keywords. These words are not currently used in JavaScript, but they are reserved by ECMAScript v3 as possible future extensions to the language.

Table 2-2. Words reserved for ECMA extensions

abstract	double	goto	native	static
boolean	enum	implements	package	super
byte	export	import	private	synchronized
char	extends	int	protected	throws
class	final	interface	public	transient
const	float	long	short	volatile
debugger

In addition to some of the formally reserved words just listed, current drafts of the ECMAScript v4 standard are contemplating the use of the keywords as, is, namespace, and use. Current JavaScript interpreters will not prevent you from using these four words as identifiers, but you should avoid them anyway. ...