@ungap/essential-weakset/esm/index.js

Essential WeakSet for legacy browsers.

/*! (c) Andrea Giammarchi - ISC */
var self = {};
try { self.WeakSet = WeakSet; }
catch (WeakSet) {
  (function (id, dP) {
    var proto = WeakSet.prototype;
    proto.add = function (object) {
      if (!this.has(object))
        dP(object, this._, {value: true, configurable: true});
      return this;
    };
    proto.has = function (object) {
      return this.hasOwnProperty.call(object, this._);
    };
    proto.delete = function (object) {
      return this.has(object) && delete object[this._];
    };
    self.WeakSet = WeakSet;
    function WeakSet() {'use strict';
      dP(this, '_', {value: '_@ungap/weakmap' + id++});
    }
  }(Math.random(), Object.defineProperty));
}
export default self.WeakSet;