I wrote a parenthetical about weak references. I wonder why I deleted it. In short: weakrefs are unlikely to appear any time soon in ES, as they open up all kinds of fun around cross-origin objects (being able to detect their approximate life-time, and that's a fairly major side-channel attack) in some lovely edge-cases.
If you have any more details about this, or even if you don't, please post to es-discuss about it. Currently there is broad consensus on TC39 to add weak references in JS in the future.
