Additional words reserved for future use by ECMAScript 3:
As of this writing, ECMAScript version 4 has not been finalized. These words are likely to be added to the reserved words list, so you should avoid using them:
These words are likely to no longer be reserved, but we recommend that you still avoid using them:
Other identifiers to avoid:
In addition, most browsers are case-sensitive, which means that they differentiate between Document and document. Internet Explorer is only sometimes case-sensitive, which means that, for example, it may not understand any difference between Document and document. Consequently, be aware that just because it works in one browser doesn't mean that it'll always work in others. Test, test, test.