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15.4 Reserved Words

Some reserved words are used by the ActionScript interpreter to denote specific built-in language features, such as statements and operators. They are reserved for use by the interpreter, and we must avoid using them as identifiers in our code. Using a reserved word for any purpose other than its reserved internal purpose causes an error in most cases. ActionScript's reserved words are listed in Table 15-1.

Table 15-1. ActionScript's reserved words

add[1]	delete	ge[1]	le[1]	onClipEvent	this
and[1]	do	gt[1]	lt[1]	or[1]	typeof
break	else	if	ne[1]	return	var
case	eq[1]	ifFrameLoaded[1]	new	super	void
continue	for	in	not[1]	switch	while
default	function	instanceof	on	tellTarget[1]	with

^[1] Flash 4 reserved words that have been deprecated as of Flash 5.

You should also try to avoid using the keywords listed in Table 15-2. They are not reserved words for ActionScript in Flash MX, but they may become a part of the language in the future, because they are slated for potential use by ECMA-262.

Table 15-2. Potential reserved words in the future

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

In addition to the formally defined reserved keywords, you should also avoid using the names of built-in properties, methods, and objects as identifiers in your code. Doing so overrides the default behavior of the property, method, or object in question.

The following is a bad idea because the Date variable overrides the built-in constructor of the same name:

Date = new Object();   // Oops! We just disabled the Date( ) constructor

Now we can no longer create Date objects:

var now = new Date( );  // Sets now to undefined
trace(now);            // Displays the empty string, not the current time and date

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