Thanks. One small thing: since you want gulp to be in your path, maybe it should be installed globally (-g) rather than locally along with the other modules.
One more: In getItems, I had to change this.items to ListStore.items. Perhaps 'this' isn't referring ListStore as we're within a 'let' rather than inside a class definition?
Another: You can't rely on items.length() to provide a unique ID. If I start with two items, and delete item 0, then items.length() will return 1. But item 1 already exists, so you will add a second item with the same key as the first, which is bad.