how JScript cleans up

From http://msdn.microsoft.com/msdnmag/issues/01/05/web/

JScript uses a mark-and-sweep garbage collector with a variety of heuristics used to determine when to run garbage collection. The JScript garbage collector works like this:

1. When the script engine is shut down, garbage is collected.
   
2. When 256 variants, or more than 64KB of strings, or more than 4096 array slots have been allocated, the garbage collector sets a flag that says collect soon.
   
3. Whenever a new statement is executed or the script debugger starts, that flag is checked, and if it is set, a collection is done.
   

There is an undocumented JScript function called CollectGarbage that forces a garbage collection. This is for testing purposes only—do not ship code that calls this function. It is a poor programming practice to write code in JScript that depends on garbage collections being done at particular times. If you need predictable garbage collection, use a language that supports it (like Visual Basic® or VBScript). Note that all of this is the implementation detail of the engine and should not be relied upon because it may change in the future. Note also that the version of JScript supported by Microsoft® .NET will use the .NET Framework garbage collector, a multigenerational mark-and-sweep collector.
And remember, if you want a deterministic-lifetime app, use a deterministic-lifetime language like C++, Visual Basic 6.0, or VBScript; not an indeterministic-lifetime language like JScript, Scheme, or Java. If you're writing a program that depends on being able to have a deterministic object lifetime, JScript is not the right tool for the job. Trying to make it a deterministic-lifetime language will just create headaches down the road.

From http://www.faqts.com/knowledge_base/view.phtml/aid/10251

This function uses ActiveX to get a forms input into a spreadsheet cell.

function xlWrite(r,c) {
  var xlApp, xlSheet;
  xlApp = new ActiveXObject("Excel.Application");
  xlApp.Visible = true;
  xlApp.Workbooks.Add();
  xlSheet = xlApp.ActiveSheet;
  xlSheet.Cells(r,c).Value = frm.txt.value;
  xlSheet.SaveAs("C://xlText.xls");

Note that Excel has a bug and doesn't shut down after calling the 
Quit() method when automating from JScript. To work around this 
problem, the CollectGarbage() method is used to force JScript's garbage 
collection to occur almost immediately.

  xlApp.Quit();
  xlApp = null;
  setTimeout("CollectGarbage()",1);
}

Beware of garbage collector. If your declare your DHTML objects inside a function, it may be garbage collected when it goes out of scope and disappears.