Most of the declarations to reference item inventory products are declared with var (I assume for JS implementations?)- what are the strict declarations for Items, Item Categories, and Item Definitions?
We use var constantly because it makes things incredibly easier when refactoring code.
The type of the variables are supposed to be obvious from their names.
If you aren't sure of the Type of a variable, or the type returned by a function, your IDE should be able to tell you when you hover over them with your mouse.
Item, ItemDefinition, ItemCategory are the types you asked about.