is-bigint 
Is this an ES BigInt value?
Example
var isBigInt = require('is-bigint');
assert(!isBigInt(function () {}));
assert(!isBigInt(null));
assert(!isBigInt(function* () { yield 42; return Infinity; });
assert(!isBigInt(Symbol('foo')));
assert(isBigInt(1n));
assert(isBigInt(Object(1n)));
Tests
Simply clone the repo, npm install, and run npm test