/* globals WeakSet */
export default (typeof WeakSet === 'function'
    ? WeakSet
    : class WeakSetPolyFill {
        constructor() {
            this._map = new WeakMap();
        }
        add(val) {
            this._map.set(val, true);
            return this;
        }
        delete(val) {
            return this._map.delete(val);
        }
        has(val) {
            return this._map.has(val);
        }
    });