property NSString : a reference to current application’s NSString
property NSLocale : a reference to current application’s NSLocale
property NSURLRequest : a reference to current application’s NSURLRequest
property NSDateFormatter : a reference to current application’s NSDateFormatter
property NSURLConnection : a reference to current application’s NSURLConnection
property NSURLRequestUseProtocolCachePolicy : a reference to current application’s NSURLRequestUseProtocolCachePolicy

tell application "Safari"
　　tell front document
　　　　set aURL to URL
　　end tell
end tell

set aURL to (current application’s |NSURL|’s URLWithString:aURL)
set {exRes, headerRes, aData} to checkURLResourceExistence(aURL, 3) of me
set aDate to headerRes’s |date| as string

set lastUpdateDate to dateFromStringWithDateFormat(aDate, "EEE, dd MMM yyyy HH:mm:ss zzz") of me
return lastUpdateDate

— 指定URLにファイル（画像など）が存在するかチェック
–> {存在確認結果（boolean）, レスポンスヘッダー(NSDictionary), データ(NSData)}
on checkURLResourceExistence(aURL, timeOutSec as real)
　　set aRequest to (NSURLRequest’s requestWithURL:aURL cachePolicy:(NSURLRequestUseProtocolCachePolicy) timeoutInterval:timeOutSec)
　　set aRes to (NSURLConnection’s sendSynchronousRequest:aRequest returningResponse:(reference) |error|:(missing value))
　　set dRes to (first item of (aRes as list))
　　set bRes to (second item of (aRes as list))
　　if bRes is not equal to missing value then
　　　　set hRes to (bRes’s allHeaderFields())
　　　　set aResCode to (bRes’s statusCode()) as integer
　　else
　　　　set hRes to {}
　　　　set aResCode to -1 –error
　　end if
　　return {(aResCode = 200), hRes, dRes}
end checkURLResourceExistence

–指定形式の日付テキストをAppleScriptのdateオブジェクトに変換
on dateFromStringWithDateFormat(dateString, dateFormat)
　　set dStr to NSString’s stringWithString:dateString
　　set dateFormatStr to NSString’s stringWithString:dateFormat
　　
　　set aDateFormatter to NSDateFormatter’s alloc()’s init()
　　aDateFormatter’s setDateFormat:dateFormatStr
　　aDateFormatter’s setLocale:(NSLocale’s alloc()’s initWithLocaleIdentifier:"en_US_POSIX")
　　
　　set aDestDate to (aDateFormatter’s dateFromString:dStr)
　　
　　return aDestDate as date
end dateFromStringWithDateFormat