The Tor Browser / file revision

 // Multiple live iterators on the same Set can cope with removing entries.

 load(libdir + "iteration.js");

 // Make a set.

 var set = Set();

 var SIZE = 7;

 for (var j = 0; j < SIZE; j++)

     set.add(j);

 // Make lots of iterators pointing to entry 2 of the set.

 var NITERS = 5;

 var iters = [];

 for (var i = 0; i < NITERS; i++) {

     var iter = set[std_iterator]();

     assertIteratorNext(iter, 0);

     assertIteratorNext(iter, 1);

     iters[i] = iter;

 }

 // Remove half of the set entries.

 for (var j = 0; j < SIZE; j += 2)

     set.delete(j);

 // Make sure all the iterators still work.

 for (var i = 0; i < NITERS; i++) {

     var iter = iters[i];

     for (var j = 3; j < SIZE; j += 2)

         assertIteratorNext(iter, j);

     assertIteratorDone(iter, undefined);

 }