JavaScript Reserved Words
In JavaScript you cannot use these reserved words as variables, labels, or function names:
| abstract | arguments | async * | 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 |
| function | 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 |
| using * | var | void | volatile |
| while | with | yield |
Note
Words marked with* have been added to JavaScript from after 2015.
You can read more the newest JavaScript versions in JS News 2025-2015.
Removed Reserved Words
The following reserved words was removed from the ECMAScript 5/6 standard:| abstract | boolean | byte | char |
| double | final | float | goto |
| int | long | native | short |
| synchronized | throws | transient | volatile |
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 |
| 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 |
