Iterable WeakSet in JavaScript

iterable_weak_map.js

// spec: https://github.com/tc39/proposal-weakrefs
// the spec contains an [iterable WeakMap implementation](https://github.com/tc39/proposal-weakrefs#iterable-weakmaps)
// NOTE: this WeakSet implementation is incomplete, only does what I needed
// In Firefox Nightly, visit about:config and enable javascript.options.experimental.weakrefs

class IterableWeakMap extends Map {
  set(k, v) {
    super.set(new WeakRef(k), v)
  }
  forEach(fn) {
    super.keys().forEach(ref => {
      const key = ref.deref()
      if (key) fn(key)
    })
  }
  *[Symbol.iterator]() {
    for (const ref of super.keys()) {
      const key = ref.deref()
      if (key) yield key
    }
  }
}

test.js

wm = new IterableWeakMap()
function showWMKeys() {
  for (k of wm) {
    console.dir(k)
   }

}

a = {b: 'c'}
wm.set(a, true)

showWMKeys()

typeof a
delete a
typeof a

showWMKeys()