michael@0: var global = 0;
michael@0: Object.defineProperty(Array.prototype, "2", {get: function() { return global++; }});
michael@0: 
michael@0: function f() {
michael@0:     var a = [];
michael@0:     var b = [0, 1, , 3];
michael@0:     for (var i=0; i<100; i++)
michael@0:         var c = a.concat(b);
michael@0:     assertEq(c[2], 99);
michael@0: }
michael@0: f();