Hi, you don't need NWjs to make multiple local storage saveslots, unless you want to create files that the player can manipulate afterward;
Once you put everything you need in your array, use Local storage plugin to set an item with array.asJson as its content, and its slot name, that way you can save item "save1", item "save2" etc, a method is to use a variable to choose with slot is selected;
To load it, you need to do the local storage correct action order : Get item "(insert slot name)", on item get, set array from Json with localstorage.ItemValue ~