es-shimsset.prototype.issupersetof 
ES Proposal spec-compliant shim for Set.prototype.isSupersetOf. Invoke its "shim" method to shim Set.prototype.isSupersetOf if it is unavailable or noncompliant.
This package implements the es-shim API interface. It works in an ES3-supported environment, and complies with the proposed spec. When shimmed, it uses es-set to shim the Set implementation itself if needed.
Most common usage:
var assert = require('assert');
var isSupersetOf = require('set.prototype.issupersetof');
var set1 = new Set([1, 2]);
var set2 = new Set([2, 3]);
var set3 = new Set([1]);
assert.equal(isSupersetOf(set1, set2), false);
assert.equal(isSupersetOf(set2, set1), false);
assert.equal(isSupersetOf(set1, set3), true);
isSupersetOf.shim();
assert.equal(set1.isSupersetOf(set2), false);
assert.equal(set2.isSupersetOf(set1), false);
assert.equal(set1.isSupersetOf(set3), true);Tests
Simply clone the repo, npm install, and run npm test