Inside Macintosh: AppleScript Language Guide / Part 2 - AppleScript Language Reference

Chapter 4 - Commands / Command Definitions

Exists application command

An Exists command is a request to determine whether the object specified by a reference exists.

SYNTAX

referenceToObject exists 
exists referenceToObject

PARAMETER

referenceToObject

A reference to the object or objects to find.
Class: Reference

RESULT

If true, all of the objects referred to by referenceToObject exist. If false, one or more of the objects referred to by referenceToObject do not exist.
Class: Boolean

EXAMPLES

tell document "Tremendous" of app "Scriptable Text Editor"   if word 7 exists then
      delete word 7
   end if
end tell
tell application "Scriptable Text Editor"   if exists front document then
      print front document
   end if
end tell