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