Creating a barebones WeakMap with node-weak (String keys only)

weakmap.js

var weak = require('weak')

// This is our weakmap; a regular JS Object
var map = {}

// This is the object we wanna store a weak reference to
var anObj = { foo: 'bar' }
  , key = 'anObj'

// Create a weak reference and store it in the map.
// Arguments:
//   1) the object to create a reference to
//   2) the callback function to call when being GC'd
//   3,4,...) Any arguments that should be given to the callback function when invoked
map[key] = weak(anObj, cleanup, key)

// function that gets called when the weak reference is being GC'd
// in this case, remove the dead weak ref from the weakmap
function cleanup (key) {
  delete map[key]
}


// Now destory the only *strong* reference to anObj
anObj = null

// Now we can retrieve the object from the weak map
weak.get(map[key])

Object.keys(map).length // 1

// Run the GC (with --expose-gc)
gc()

// and after the GC runs, anObj will no longer be in the weakmap
Object.keys(map).length // 0