@ungap/weakset/index.js

WeakSet for IE11 and engines with a WeakMap

/*! (c) Andrea Giammarchi - ISC */
var self = this || {};
try { self.WeakSet = WeakSet; }
catch (WeakSet) {
  // requires a global WeakMap (IE11+)
  (function (WeakMap) {
    var all = new WeakMap;
    var proto = WeakSet.prototype;
    proto.add = function (value) {
      return all.get(this).set(value, 1), this;
    };
    proto.delete = function (value) {
      return all.get(this).delete(value);
    };
    proto.has = function (value) {
      return all.get(this).has(value);
    };
    self.WeakSet = WeakSet;
    function WeakSet(iterable) {
      'use strict';
      all.set(this, new WeakMap);
      if (iterable)
        iterable.forEach(this.add, this);
    }
  }(WeakMap));
}