JScript has a number of reserved words that you cannot use as identifiers. Reserved words have a specific meaning to the JScript language, as they are part of the language syntax. Using a reserved word causes a compilation error when loading your script.
JScript also has a list of future reserved words. These words are not currently part of the JScript language, although they are reserved for future use.
Reserved Words
| break | delete | function | return | typeof |
| case | do | if | switch | var |
| catch | else | in | this | void |
| continue | false | instanceof | throw | while |
| debugger | finally | new | true | with |
| default | for | null | try |
| abstract | double | goto | native | static |
| boolean | enum | implements | package | super |
| byte | export | import | private | synchronized |
| char | extends | int | protected | throws |
| class | final | interface | public | transient |
| const | float | long | short | volatile |
When choosing identifiers it is also important to avoid any words that are already the names of intrinsic JScript objects or functions, such as String or parseInt.