1391116 - WeakMap does not accept an instance of SVGAnimatedLength as a key

Status: RESOLVED DUPLICATE of bug 1351501

(Core :: DOM: Bindings (WebIDL), defect, P3)

Description

[ravi.jayaramappa]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/603.3.8 (KHTML, like Gecko) Version/10.1.2 Safari/603.3.8

Steps to reproduce:

var mySvg = document.createElementNS('http://www.w3.org/2000/svg', 'svg');
console.log(typeof mySvg.width); // Will log as object
var map = new WeakMap();
map.set(mySvg.width, "foo"); //Fails in Firefox with this error "TypeError: cannot use the given object as a weak map key"


Actual results:

Throws a TypeError with the following message "TypeError: cannot use the given object as a weak map key"

Same works as expected on Google Chrome and Safari


Expected results:

Should have added the SVGAnimatedLength instance to weakmap.

Comment 1

[Tooru Fujisawa [:arai]]

I guess it's problem in somewhere near here
https://dxr.mozilla.org/mozilla-central/rev/7ff4c2f1fe11f6b98686f783294692893b1e1e8b/dom/bindings/BindingUtils.cpp#1064-1083

Comment 2

[Andrew Overholt [:overholt]]

Peter, is this expected to work? mccr8 was speculating that maybe the SVG stuff is on the old bindings ...

Comment 3

[Peter Van der Beken [:peterv]]

It's on the new bindings, it's wrappercached but it's not derived from nsISupports. As explained in TryPreserveWrapper, we don't have a way to know if it's wrappercached, because it's not derived from nsISupports. So we can't preserve the wrapper and the weakmap code relies on preserving the wrapper.

We could fix this by having a generated hook that casts the native object to nsWrapperCache.