lib/index.esm.js
function get(key) {
    if (_isObject(key)) {
      var data = getWeak(key);
      if (data === true) return uncaughtFrozenStore(_validateCollection(this, WEAK_MAP)).get(key);
      return data ? data[this._i] : undefined;
    }
  }
function get(key) {
    if (_isObject(key)) {
      var data = getWeak(key);
      if (data === true) return uncaughtFrozenStore(_validateCollection(this, WEAK_MAP)).get(key);
      return data ? data[this._i] : undefined;
    }
  }
23.3.3.3 WeakMap.prototype.get(key)