1328835 - Unable to define a getter on dataset objects

Status: RESOLVED DUPLICATE of bug 1301754

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

Description

[Jan de Mooij [:jandem]]

Noticed this while writing tests for bug 965992.

The test below alerts |123| and |number| in Safari and Chrome. In Firefox, however, I get |undefined| and |string|. We seem to define a data property with value "undefined" instead of the getter?

<script>
var o = document.documentElement.dataset;
Object.defineProperty(o, "foobar", {get: function() { return 123; }});
alert(o.foobar);
alert(typeof o.foobar);
</script>

Comment 1

[:Ms2ger (he/him; ⌚ UTC+1/+2)]

I imagine the bug here is that we do 

    if (!ConvertJSValueToString(cx, desc.value(), eStringify, eStringify, value)) {

in DOMProxyHandler::defineProperty without checking desc.isDataDescriptor(), while the WebIDL standard states

> If the result of calling IsDataDescriptor(Desc) is false, then return false.

at https://heycam.github.io/webidl/#legacy-platform-object-defineownproperty step 2.2.2.1.

Comment 2

[Boris Zbarsky [:bzbarsky]]

Oh.  Right.  This thing has a named setter/creator, so using it for accessor props for the bug 965992 tests is not a good idea.  I had forgotten about that part.

Per spec, that defineProperty call should throw.  Bug 1301754 tracks the fact that we don't throw; https://bugs.chromium.org/p/chromium/issues/detail?id=645542 is the Chromium bug.

For the tests in bug 965992, probably best to just use an HTMLFormElement instead; I'm pretty sure that will not switch away from its current shadowing behavior (which I can't say for document).  So:

  <!DOCTYPE html>
  <form></form>
  <script>
     var form = document.querySelector("form");
  </script>