如何在AutoIt中读取其值之前测试对象上是否存在属性？(How to test if object property exists before reading its value?)

 如果页面是PDF文件，我有一个IE对象$ oIE，它不会让我访问页面的主体。 
 
 如果我尝试访问变量，我的代码会中断。 以下是我如何称呼它： 
 
_IEAction($oIE, 'saveas')
 
 但是这个消息错误了： 
 
"C:\Program Files (x86)\AutoIt3\Include\IE.au3" (1959) : ==> The requested action with this object has failed.:
$oObject.document.execCommand("SaveAs")
$oObject.document^ ERROR
 
 我需要遍历几页PDF并将它们保存到磁盘。 仅当页面是PDF时才会抛出此错误，当它是普通的HTML页面时，它可以正常工作。 
 
 有没有办法检查文档主体是否存在？ 如果它不存在，它告诉我该页面是PDF，我需要保存它。 

My Internet Explorer object $oIE, won't let me access the page's body property if it concerns a PDF file (as opposed to a HTML page). If I try to access that property, my code breaks. Here is how I call it:
 
_IEAction($oIE, 'saveas')
 
But it errors:
 
"C:\Program Files (x86)\AutoIt3\Include\IE.au3" (1959) : ==> The requested action with this object has failed.:
$oObject.document.execCommand("SaveAs")
$oObject.document^ ERROR
 
I need to iterate over a few pages of PDF files and save them to disk. This error is thrown only when the page is a PDF document; a normal HTML page works fine. How to check if the document body property exists? If it doesn't, it means the page is a PDF (I need to save it).

原文：https://stackoverflow.com/questions/32977365