The Tor Browser / file revision

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

 load(libdir + "iteration.js");

 // Make a map.

 var map = Map();

 var SIZE = 7;

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

     map.set(j, j);

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

 var NITERS = 5;

 var iters = [];

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

     var iter = map[std_iterator]();

     assertIteratorNext(iter, [0, 0]);

     assertIteratorNext(iter, [1, 1]);

     iters[i] = iter;

 }

 // Remove half of the map entries.

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

     map.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, j]);

     assertIteratorDone(iter, undefined);

 }