michael@0: // for-in loops on Maps and Sets enumerate properties.
michael@0: 
michael@0: var test = function test(obj) {
michael@0:     assertEq(Object.keys(obj).length, 0);
michael@0: 
michael@0:     var i = 0, v;
michael@0:     for (v in obj)
michael@0:         i++;
michael@0:     assertEq(i, 0);
michael@0: 
michael@0:     obj.ownProp = 1;
michael@0:     assertEq(Object.keys(obj).join(), "ownProp");
michael@0: 
michael@0:     for (v in obj)
michael@0:         i++;
michael@0:     assertEq(i, 1);
michael@0:     assertEq(v, "ownProp");
michael@0: 
michael@0:     delete obj.ownProp;
michael@0: };
michael@0: 
michael@0: test(Map.prototype);
michael@0: test(new Map);
michael@0: test(Set.prototype);
michael@0: test(new Set);