TypeScript: make field public only for special classes

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Here's a problem. I work with pattern MVVM, which means I have some Views with display logic only and some ViewModels with functional logic only. ViewModels has methods and fields. And these fields and methods can be read or called by other ViewModel or by the View of ViewModel.

And I'd like to know, is there a way to make some fields visible only in View, but hidden (private) in other ViewModels?

I need something like this:

class ViewModel1 {
  doSomething = () => {...}; // can be called anywhere

  publicForView doSomethingInView = () => {...}; // can be called only in the View

  private doSomethingInViewModel = () => {...}; // can be called only here
}

// view is a HOC-function, which joins ViewModel with View
const View1 = view(ViewModel1, ({ viewModel }) => {
  viewModel.doSomethingInView(); // can be called
  viewModel.doSomething(); // can be called
  viewModel.doSomethingInViewModel(); // can't be called

  return <div/>;
});

class ViewModel2 {
  private viewModel1: ViewModel1;

  constructor() {
    viewModel.doSomethingInView(); // can't be called
    viewModel.doSomething(); // can be called
    viewModel.doSomethingInViewModel(); // can't be called
  }
}
typescript reactjs mvvm oop javascript
1 Answers

If you want a class in Typescript to expose only certain parts of a class you can create interfaces, so save on duplicate code using Pick / Omit will help in creating the interfaces.

eg..

class ViewModel {
  doSomething = () => {};  
  doSomethingInView = () => {}
  doSomethingInViewModel = () => {}
}

type View = Omit<ViewModel, 'doSomethingInViewModel'>
type Model = Omit<ViewModel, 'doSomethingInView'>

function doSomethingWithView(view: View) {
    view.doSomething();
    view.doSomethingInView();
    //view.doSomethingInViewModel();  will error
}

function doSomethingWidthModel(model: Model) {
    model.doSomething();
    model.doSomethingInViewModel();
    // view.doSomethingInView(); will error
}

const view = new ViewModel();
//we can pass view to both functions, but the methods will be restricted
doSomethingWithView(view);
doSomethingWidthModel(view);

Working example here -> TS Playground

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