Create a function that takes a function and props, calls that function with the props then calls mergeStyleSets on the result. Weakly typed function signature since scala does not have structural typing. We can do better at some point even without structural typing. This does not work on a straight IStyleSet since that's set as a dictionary (string->IStyle) but instead an object type IStyleSetTag. Ultimately, given a style function or style object and a set of properties that are either input into the style function or are properties to be merged with the first argument if its an object and not a function, return a set of classnames that represent style processing via 'mergeStyleSets'.

You usually call this inside your component object with a styles function (props=>styles) and properties passed in as props so that they are all merged together to generate your classnames linked to stylesheet styles. You need to tag your js.Object derived traits with IStyleSetTag and IClassNamesTag to drive type recognition.

You are probably better off just defining your own getClassNames (and memoizing it) and calling mergeStyleSets yourself. Your getClassNames can take a styles (function or object) parameter.

This is another tough one to type in scala.js. If you use a scala function to define f, an implicit will convert it to a js function automatically. Or you can use js.Any.fromFunctionN() to be explicit which you sometimes need to do to get the scala function to js function conversion correct.