is-finalizationregistry 
Is this value a JS FinalizationRegistry? This module works cross-realm/iframe, and despite ES6 @@toStringTag.
Example
var isFinalizationRegistry = require('is-finalizationregistry');
assert(!isFinalizationRegistry(function () {}));
assert(!isFinalizationRegistry(null));
assert(!isFinalizationRegistry(function* () { yield 42; return Infinity; });
assert(!isFinalizationRegistry(Symbol('foo')));
assert(!isFinalizationRegistry(1n));
assert(!isFinalizationRegistry(Object(1n)));
assert(!isFinalizationRegistry(new Set()));
assert(!isFinalizationRegistry(new WeakSet()));
assert(!isFinalizationRegistry(new Map()));
assert(!isFinalizationRegistry(new WeakMap()));
assert(!isFinalizationRegistry(new WeakRef({})));
assert(isFinalizationRegistry(new FinalizationRegistry(function () {})));
class MyFinalizationRegistry extends FinalizationRegistry {}
assert(isFinalizationRegistry(new MyFinalizationRegistry(function () {})));
Tests
Simply clone the repo, npm install, and run npm test