788966 - Error when calling inherited XMLHttpRequest methods

Status: RESOLVED INVALID

(Core :: DOM: Core & HTML, defect)

Description

[Phil]

User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:13.0) Gecko/20120606 Firefox/13.0
Build ID: 20120606130836

Steps to reproduce:

Run the following Javascript code in Firefox 14+:

try{
    var xhrConstructor = function() {};
    xhrConstructor.prototype = new XMLHttpRequest();
    var foo = new xhrConstructor();
    foo.addEventListener('load', function() {}, false);
}catch(e){alert(e.toString())}



Actual results:

In Firefox 14+, an error is thrown when addEventListener is called:

[Exception... "Could not convert JavaScript argument"  nsresult: "0x80570009 (NS_ERROR_XPC_BAD_CONVERT_JS)"  location: "JS frame :: Scratchpad :: <TOP_LEVEL> :: line 5"  data: no]

It isn't limited to addEventListener, all other methods inherited from XMLHttpRequest also fail.


Expected results:

The same behaviour as in Firefox < 14, the object should function as an XMLHttpRequest object, and no error should be thrown.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Per WebIDL spec, this should throw.

Comment 2

[Boris Zbarsky [:bzbarsky]]

And note that browser behavior here was inconsistent, so it's not like any actual web sites that want to work cross-browser were using this pattern...

Comment 3

[Oleg Torbasow]

(In reply to Boris Zbarsky (:bz) from comment #1)
> Per WebIDL spec, this should throw.

Could you tell any more on this issue, please?

Comment 4

[Boris Zbarsky [:bzbarsky]]

I'm not sure what more there is to tell.  See http://dev.w3.org/2006/webapi/WebIDL/#es-operations the description of the Function object step 2.