JavaScript Reserved Words

JavaScript Reserved Words

In JavaScript you cannot use these reserved words as variables, labels, or function names:
abstract arguments await* 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 ECMAScript 5 and 6.

You can read more about the different JavaScript versions in the chapter JS Versions.

Removed Reserved Words

The following reserved words has been removed from the ECMAScript 5/6 standard:
abstract boolean byte char
double final float goto
int long native short
synchronized throws transient volatile

Do not use these words as variables. ECMAScript 5/6 does not have full support in all browsers.

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

Other Reserved Words

JavaScript can be used as the programming language in many applications.

You should also avoid using the name of HTML and Window 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

HTML Event Handlers

In addition you should avoid using the name of all HTML event handlers.

onblur onclick onerror onfocus
onkeydown onkeypress onkeyup onmouseover
onload onmouseup onmousedown onsubmit