which-collection 
Which kind of Collection (Map, Set, WeakMap, WeakSet) is this JavaScript value? Works cross-realm, without instanceof, and despite Symbol.toStringTag.
Example
var whichCollection = require('which-collection');
var assert = require('assert');
assert.equal(false, whichCollection(undefined));
assert.equal(false, whichCollection(null));
assert.equal(false, whichCollection(false));
assert.equal(false, whichCollection(true));
assert.equal(false, whichCollection([]));
assert.equal(false, whichCollection({}));
assert.equal(false, whichCollection(/a/g));
assert.equal(false, whichCollection(new RegExp('a', 'g')));
assert.equal(false, whichCollection(new Date()));
assert.equal(false, whichCollection(42));
assert.equal(false, whichCollection(NaN));
assert.equal(false, whichCollection(Infinity));
assert.equal(false, whichCollection(new Number(42)));
assert.equal(false, whichCollection(42n));
assert.equal(false, whichCollection(Object(42n)));
assert.equal(false, whichCollection('foo'));
assert.equal(false, whichCollection(Object('foo')));
assert.equal(false, whichCollection(function () {}));
assert.equal(false, whichCollection(function* () {}));
assert.equal(false, whichCollection(x => x * x));
assert.equal(false, whichCollection([]));
assert.equal('Map', whichCollection(new Map()));
assert.equal('Set', whichCollection(new Set()));
assert.equal('WeakMap', whichCollection(new WeakMap()));
assert.equal('WeakSet', whichCollection(new WeakSet()));
Tests
Simply clone the repo, npm install, and run npm test
