JScript has a number of reserved keywords. These words come in three types: JScript reserved keywords, those from Java, and words to avoid.

JScript Keywords

break	for	new	true	with
continue	function	null	typeof
else	if	return	var
false	in	this	while

 

Java Reserved Keywords

abstract	default	implements	static	void
boolean	do	import	super
byte	double	instanceof	switch
case	extends	int	synchronized
catch	final	interface	throw
char	finally	long	throws
class	float	native	transient
const	goto	package	try

The words to avoid are any that are already objects or static functions. Words like String or parseInt are included in this.

Using any of the keywords from the first two categories causes a compilation error when your script is first loaded. Using a reserved word from the third set can cause odd behavior problems if you attempt to use both your variable and the original entity of the same name in the same script. For example, the following script does not do quite what you think it should:

var String;
var text = new String("This is a string object");

In this case, you get an error saying that String is not an object. Many cases of using a pre-existing identifier aren't this obvious.