is-shared-array-buffer 
Is this value a JS SharedArrayBuffer? This module works cross-realm/iframe, does not depend on instanceof or mutable properties, and despite ES6 Symbol.toStringTag.
Example
var assert = require('assert');
var isSharedArrayBuffer = require('is-shared-array-buffer');
assert(!isSharedArrayBuffer(function () {}));
assert(!isSharedArrayBuffer(null));
assert(!isSharedArrayBuffer(function* () { yield 42; return Infinity; });
assert(!isSharedArrayBuffer(Symbol('foo')));
assert(!isSharedArrayBuffer(1n));
assert(!isSharedArrayBuffer(Object(1n)));
assert(!isSharedArrayBuffer(new Set()));
assert(!isSharedArrayBuffer(new WeakSet()));
assert(!isSharedArrayBuffer(new Map()));
assert(!isSharedArrayBuffer(new WeakMap()));
assert(!isSharedArrayBuffer(new WeakRef({})));
assert(!isSharedArrayBuffer(new FinalizationRegistry(() => {})));
assert(!isSharedArrayBuffer(new ArrayBuffer()));
assert(isSharedArrayBuffer(new SharedArrayBuffer()));
class MySharedArrayBuffer extends SharedArrayBuffer {}
assert(isSharedArrayBuffer(new MySharedArrayBuffer()));
Tests
Simply clone the repo, npm install, and run npm test