Why is my onbeforeunload handler causing an “Unspecified error” error?

Question

I am using the following JavaScript function within IE6:

window.onbeforeunload = function() {  
  if (itemChanged) {  
     return 'You have made changes to data on this page.  If you navigate away from this page without first saving your data, the changes will be lost.';  
  }  
};  

But when I press the Cancel button on the dialog, I am getting a JavaScript page error:

Error: Unspecified error.

Any ideas?

Answer 1

Check your value of (itemChanged). Is it possible something else causes the error? It works fine for me.

Jsbin sample.