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Conditional Compilation Variables

The following predefined variables are available for conditional compilation.

Variable

Description

@_win32

true if running on a Win32 system and the /platform option is not specified or the /platform:anycpu option is specified, otherwise NaN.

@_win16

true if running on a Win16 system, otherwise NaN.

@_mac

true if running on an Apple Macintosh system, otherwise NaN.

@_alpha

true if running on a DEC Alpha processor, otherwise NaN.

@_x86

true if running on an Intel processor and the /platform option not specified or /platform:anycpu option is specified, otherwise NaN.

@_mc680x0

true if running on a Motorola 680x0 processor, otherwise NaN.

@_PowerPC

true if running on a Motorola PowerPC processor, otherwise NaN.

@_jscript

Always true.

@_jscript_build

The build number of the JScript scripting engine.

@_jscript_version

A number representing the JScript version number in major.minor format.

@_debug

true if compiled in debug mode, otherwise false.

@_fast

true if compiled in fast mode, otherwise false.

NoteNote

The version number reported for JScript .NET is 7.x. The version number reported for JScript 8.0 is 8.x.

Before using a conditional compilation variable, conditional compilation must be turned on. The @cc_on statement can turn on conditional compilation. Conditional compilation variables are often used in scripts written for Web browsers. It is not so common to use conditional compilation variables in scripts written for ASP or ASP.NET pages or command-line programs since the capabilities of the compilers can be determined using other methods.

When writing a script for a Web page, always place conditional compilation code in comments. This allows hosts that do not support conditional compilation to ignore it. Here is an example.

/*@cc_on
  document.write("JScript version: " + @_jscript_version + ".<BR>");
  @if (@_win32)
     document.write("Running on 32-bit Windows.<BR>");
  @elif (@_win16)
     document.write("Running on 16-bit Windows.<BR>");
  @else
     document.write("Running on a different platform.<BR>");
  @end
@*/

Conditional compilation variables can be used to determine the version information of the engine interpreting a script. This allows a script to take advantage of the features available in the latest versions of JScript while maintaining backwards compatibility. For more information, see Detecting Browser Capabilities.

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