The arrays with holes are called Sparse Arrays, I googled for 'sparse array v8 performance' and didn't find much, but I've previously seen a Google Presentation

The arrays with holes are called Sparse Arrays, I googled for 'sparse array v8 performance' and didn't find much, but I've previously seen a Google Presentation on a slide-sharing site that did mention how poor sparse arrays perform when compared to normal contiguous arrays.