787262 - re-defineProperty on Window fails when enumerable unspecified

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[Felix Lee]

Attachment: example.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:15.0) Gecko/20100101 Firefox/15.0
Build ID: 20120821170930

Steps to reproduce:

<script>
  Object.defineProperty(window, 'x', {configurable: false, enumerable: true});
  try {
    Object.defineProperty(window, 'x', {});     // fails
  } catch (e) { console.log(e); }

  var o = {};
  Object.defineProperty(o, 'x', {configurable: false, enumerable: true});
  try {
    Object.defineProperty(o, 'x', {});          // works
  } catch (e) { console.log(e); }
</script>



Actual results:

The console shows that
  Object.defineProperty(window, 'x', {});
fails with "TypeError: can't redefine non-configurable property 'x'", but
  Object.defineProperty(o, 'x', {});
succeeds.


Expected results:

Both defineProperty calls should succeed.  Ecma-262 5th edition, section 8.12.9, when the new property descriptor lacks a value for enumerable, it doesn't matter what the current enumerable value is, because it won't be modified.

Comment 1

[Boris Zbarsky [:bzbarsky]]

I wonder whether this has to do with Window being a proxy...

Comment 2

[Jeff Walden [:Waldo]]

Seems likely.

Comment 3

[Mark S. Miller]

What is the status of this?

Comment 4

[Boris Zbarsky [:bzbarsky]]

Eric, do you have time to take a look at this?

Comment 5

[Jason Orendorff [:jorendorff]]

I think this bug was fixed a while ago. -> RESO WORKSFORME.

Recently we deliberately broke the first line of the example, the setup line:

    Object.defineProperty(window, 'x', {configurable: false, enumerable: true});
    TypeError: Not allowed to define a non-configurable property on the WindowProxy object

The combination of ES6 object invariants and age-old window object behavior implies this TypeError. ES6 says non-configurable properties can't go away; but all of a window object's properties go away when the window navigates.