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 |