Suggestion - readonly state proxy

[benallfree]

This is more a dx issue, but I see a pattern frequently where I'd like to be able to bind to a state var, but prevent accidental writes to it because writes should be handled by a helper that adjusts multiple state variables or performs other side effects. It would be nice to have something like State.readonly() that returned a wrapped version where get stateVar.val worked but set stateVar.val threw an exception.

It might look something like this:

  "readonly"() {
    let _this=this
    return { 
      ..._this,
      set "val"(v) { throw new Error(`State is read-only`) },
    }
  }

export type State<T> = {
  val: T
  onnew(l: (val: T, oldVal: T) => void): void
  readonly(): State<T> & { readonly val:T}
}

Or, if you don't want to actually add that to the code, I can basically get what I need from TS type checking

export type ReadOnlyState<T> = Omit<State<T>, 'val'> & { readonly val: T }
export const toReadOnlyState = <T>(state: State<T>) => state as ReadOnlyState<T>

[Tao-VanJS]

I think StateView<T> is exactly the TypeScript type that you're looking for.

[Tao-VanJS]

Also, I think you can have a readonly(s: State<T>) helper function by your own.