What happens when invoking `WeakRef.deref()` on a `WeakCell`?

[tc39]

What happens when invoking `WeakRef.deref()` on a `WeakCell`?

[tschneidereit]

In my polyfill I have a brand check to make deref only work for WeakRef, not WeakCell. Without such a check WeakCell wouldn't make all that much sense, I think.

[erights]

Great catch! Yes, we need to fix this.

Example code to clarify the question:

WeakRef.prototype.deref.call(wc);

where wc is a WeakCell. This code should throw, not succeed.

[ljharb]

Indeed, I’d think WeakRef would need a second internal slot, and then it and WeakCell would share the first one, and most methods would need to brand check the appropriate slot.

[littledan]

The current specification and explainer does not maintain the distinction between WeakRef and WeakCell. Closing, as this issue no longer seems relevant.