michael@0: var arr = [1];
michael@0: Object.defineProperty(arr, 1, { value: undefined, configurable: false });
michael@0: 
michael@0: // no particular reason for 9 -- just enough to trigger property-cache code,
michael@0: // maybe start JITting a little
michael@0: for (var y = 0; y < 9; y++)
michael@0:   arr.length = 1;