Updated setState to support updateFn to work with both updater function and state

[mainendra]

Currently updateFn is throwing an error when trying to setState directly without using function. e.g.

const countStore = new Store(1, {
    updateFn: prevState => updater => {
        return updater(prevState) + prevState;
    }
});
countStore.setState(1) // error
countStore.setState(() => 1) // success

Updated setState to support that. Also we should not allow user to update Updater type so, remove TUpdater.

[jiji-hoon96]

I just wanted to share a quick thought based on our Discord conversation.
I'm not a maintainer of this project. Just another community member sharing some technical observations.
Thanks for taking the time to consider my perspective in detail!

[jiji-hoon96]

When updater is a function, updater: (prev: TState) => TState

this.options.updateFn(this.prevState)(() => updater)

The type of () => updater is () => (prev: TState) => TState, but updateFn expects a parameter of type (prev: TState) => TState.

When updater is a value, updater: TState

this.options.updateFn(this.prevState)(() => updater)

The type of () => updater is () => TState, but updateFn expects a parameter of type (prev: TState) => TState.

It seems like this might cause a type error. Am I missing something?

[jiji-hoon96]

setState(updater: TState | ((prevState: TState) => TState)): void {
  this.prevState = this.state
  
  if (this.options?.updateFn) {
    // When updateFn is defined: always convert the updater to a function.
    const functionUpdater = isUpdaterFunction(updater) 
      ? updater 
      : (prev: TState) => updater
    this.state = this.options.updateFn(this.prevState)(functionUpdater)
  } else {
    // When updateFn is not defined: handle the updater directly.
    this.state = isUpdaterFunction(updater) 
      ? updater(this.prevState) 
      : updater
  }
}

If I were to make changes, I think this could be a possible improvement. What do you think?

[mainendra]

So, we need to check both whether updater is a function or not and updateFn is defined or not. Either way is fine: we can check updater’s function type first and then updateFn, or vice versa.

[jiji-hoon96]

If you have the time, I’d really appreciate hearing your thoughts on this, @tannerlinsley.
I value your perspective as the maintainer of the project.