A polyfill for IE11 or browsers that have a WeakMap, but not a WeakSet.

• CDN via https://unpkg.com/@ungap/weakset
• ESM via import WeakSet from '@ungap/weakset'
• CJS via const WeakSet = require('@ungap/weakset')

Compatible down to IE9, works well with ES5 shim upfront in IE8 (and maybe lower too).

Live test