Latest web development tutorials

×

JS Tutorial

JS HOME JS Introduction JS Where To JS Output JS Syntax JS Statements JS Comments JS Variables JS Operators JS Arithmetic JS Assignment JS Data Types JS Functions JS Objects JS Scope JS Events JS Strings JS String Methods JS Numbers JS Number Methods JS Math JS Dates JS Date Formats JS Date Methods JS Arrays JS Array Methods JS Booleans JS Comparisons JS Conditions JS Switch JS Loop For JS Loop While JS Break JS Type Conversion JS RegExp JS Errors JS Debugging JS Hoisting JS Strict Mode JS Style Guide JS Best Practices JS Mistakes JS Performance JS Reserved Words JS JSON

JS Forms

Forms Validation Forms API

JS Object

Object Definitions Object Properties Object Methods Object Prototypes

JS Functions

Function Definitions Function Parameters Function Invocation Function Closures

JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML DOM CSS DOM Animations DOM Events DOM EventListener DOM Navigation DOM Nodes DOM Nodelist

JS Browser BOM

JS Window JS Screen JS Location JS History JS Navigator JS Popup Alert JS Timing JS Cookies

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser JS Quiz JS Summary

JS References

JavaScript Objects HTML DOM Objects

JavaScript Reserved Words

❮ Previous Next Chapter ❯

In JavaScript, some identifiers are reserved words and cannot be used as variables or function names.

JavaScript Standards

ECMAScript 3 (ES3) was released in December 1999.

ECMAScript 4 (ES4) was abandoned.

ECMAScript 5 (ES5) was released in December 2009.

ECMAScript 6 (ES6) was released in June 2015, and is the latest official version of JavaScript.

Time passes, and we are now beginning to see complete support for ES5/ES6 in all modern browsers.

JavaScript Reserved Words

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

abstract	arguments	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
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	var	void	volatile
while	with	yield

Words marked with* are new in ECMAScript5

JavaScript Objects, Properties, and Methods

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

Java Reserved Words

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

Windows Reserved Words

JavaScript can be used outside HTML. It can be used as the programming language in many other applications.

In HTML you must (for portability you should) avoid using the name of HTML and Windows 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

HTML Event Handlers

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

❮ Previous Next Chapter ❯