JScript Reserved Words
JScript has a number of reserved words that have a specific meaning in the JScript language syntax. Consequently, these words are not good choices for names of functions, variables, or constants in scripts. There are three classes of reserved words.
Protected Reserved Words
Protected reserved keywords cannot be used as identifiers. Using a protected reserved word as an identifier causes a compilation error when loading your script.
Note Although "export" is a protected reserved word, it has no implementation.
New Reserved Words
JScript also has a list of new reserved words. Like protected reserved words, these keywords have special meaning within the current version of JScript. For backwards compatibility reasons, new reserved words can be used as an identifiers. Once a new reserved word is used as an identifier, it loses its meaning as a keyword in the script. Using new reserved words as identifiers can cause confusion and should be avoided.
Future Reserved Words
JScript has a list of future reserved words, which are proposed as keywords in future extensions of JScript. Like the new reserved words, these may be used as identifiers in the current version of JScript. However, by avoiding these words, it will be easier to update scripts to take advantage of the features in upcoming versions of JScript.
When choosing identifiers it is also important to avoid words that are already the names of intrinsic JScript objects or functions, such as String or parseInt.