What is the difference with types.model and types.frozen there ?

[Bittttter]

Good lucky everyone!
I need some help.
My question is that how to explain this case followed:

const App = types
    .model({
        test: t.frozen({}), // working!
        // test: types.model({}), // doesn't working oops...
    })
    .actions(self => ({
        setTest(newTest: any = {}) {
            self.test = newTest;
        },
    }));

When I call the action yet, I can modify the test field when I use types.frozen, but types.model can't. What's the difference with these, Why can not update value when use types.model

[Bittttter]

Lol. This is because MobX only tracked with definite properties, so that when I need a data structure as like followed:

interface DS {
    [key: string]: number;
}

MobX can't observed it or I should say MST doesn't support it where use by types.model. Of course I can via types.frozen<Record<string, number>>({}) to mark types and observed the observable.