weak-value/README.md

A Map with weakly referenced values, instead of keys

# WeakValue


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A Map with weakly referenced values, instead of keys, with an optional *onValueCollected* callback to pass aslong.

In Node.js, it requires [V8 release v8.4](https://v8.dev/blog/v8-release-84) or greater.

```js
import WeakValue from 'weak-value';
// const WeakValue = require('weak-value');

const wv = new WeakValue;

(() => {
  const value = {};
  wv.set('any-key', value, /* optional */ (key, map) => {
    // will log "any-key value collected" once GC kicks in
    console.log(key, 'value collected');
    console.log(map === wv);  // true
  });
})();
```

Please note that explicit `wv.delete(key)` will *NOT* invoke *onValueCollected*, as deleting a key does not mean its referenced value has been collected.