universal-weak-map.js

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src/tuple.js src/universal-weak-map.js src/util.js

universal-weak-map.js
¶

A map data structure that holds object keys weakly, yet can also hold non-object keys, unlike the native WeakMap.
```
export class UniversalWeakMap {
  constructor() {
```
¶

Since a WeakMap cannot hold primitive values as keys, we need a backup Map instance to hold primitive keys. Both this._weakMap and this._strongMap are lazily initialized.
```
    this._weakMap = null;
    this._strongMap = null;
  }
```

Since get and set are the only methods used, that’s all I’ve implemented here.

  get(key) {
    const map = this._getMap(key, false);
    if (map) {
      return map.get(key);
    }
  }

  set(key, value) {
    this._getMap(key, true).set(key, value);

An actual Map or WeakMap would return this here, but returning the value is more convenient for the tuple implementation.

    return value;
  }

  _getMap(key, canCreate) {
    if (! canCreate) {
      return isObjRef(key) ? this._weakMap : this._strongMap;
    }
    if (isObjRef(key)) {
      return this._weakMap || (this._weakMap = new WeakMap);
    }
    return this._strongMap || (this._strongMap = new Map);
  }
}

function isObjRef(value) {
  switch (typeof value) {
  case "object":
    if (value === null) {
      return false;
    }
  case "function":
    return true;
  default:
    return false;
  }
}