JavaScript Reserved Words

JavaScript Reserved Words

In JavaScript, you cannot use these keywords as variable names, identifiers, 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

Keywords marked with an asterisk are new in ECMAScript 5 and 6.

You can find more information on JS VersionRead more about different JavaScript versions here.

Removed keywords

The following keywords have been removed from the ECMAScript 5/6 standard:

abstract boolean byte char
double final float goto
int long native short
synchronized throws transient volatile

Please do not use these reserved words as variable names. Not all browsers fully support ECMAScript 5/6.

JavaScript objects, properties, and methods

You should also avoid using the names 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 with Java. You should avoid using certain Java objects and properties as JavaScript identifiers:

getClass java JavaArray javaClass
JavaObject JavaPackage

Other reserved words

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

You should also avoid using the names 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
window

HTML Event Handler

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

For example:

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