javascript Operators @cc_on

The "conditional" part comes from numerous global properties (all preceded with the @ symbol) that reveal environmental properties, such as script engine version, operating system, and CPU type. All of this information is available from the navigator object's properties on a wide range of browsers, so this is not unique information available only to this conditional environment.

To engage conditional compilation, include the following statement in your script:

/*@cc_on @*/

This is a one-way toggle: once the mode is turned on, it can't be turned off in the current page.

The following fragment shows how the @if and related statements display some environmental information in the window's status bar if the browser is running JScript Version 5.6 or later (IE 6 or later):

/*@cc_on @*/
/*@if (@_jscript_version>= 5.6 && @_x86)
  status = "Now running JScript version " + @_jscript_version + 
  " with Intel inside.";
  @else @*/
  status = "Have a nice day.";
/*@end @*/ 

The @set statement lets you assign a numeric or Boolean value (no strings) to a variable (a variable with an @ prefix) within a conditional compilation section:

@set @isOK = @_win32

Once initialized, that variable (including its otherwise unacceptable identifier) can be used in script statements throughout the page. Note that the Visual Basic-inspired syntax of @ statements in conditional compilation statements does not permit semicolons at the end of statements.

On the one hand, conditional compilation could be useful for IE-only deployment to screening older IE versions from new language features that would generate compilation errors (such as try-catch constructions) because such statements compile only under very controllable version situations. In a multibrand browser development shop, however, at most you might find application for IE-only debugging purposes, but probably not for actual application deployment.

See the discussion above.