The Tor Browser / file revision

 // set.keys() and set.values() return iterators over the elements

 // and set.entries() returns an iterator that yields pairs [e, e].

 load(libdir + "iteration.js");

 var data = [1, 2, 3, 4];

 var s = Set(data);

 var ki = s.keys();

 assertIteratorNext(ki, 1);

 assertIteratorNext(ki, 2);

 assertIteratorNext(ki, 3);

 assertIteratorNext(ki, 4);

 assertIteratorDone(ki, undefined);

 assertEq([...s.keys()].toSource(), data.toSource());

 assertEq([...s.values()].toSource(), data.toSource());

 assertEq([...s.entries()].toSource(), [[1, 1], [2, 2], [3, 3], [4, 4]].toSource());