typed-vuex.ts

import * as Vuex from 'vuex'

type GettersOption<S> = { [key: string]: (state: S) => unknown }

type Store<S, M, A, G extends GettersOption<S>> = {
  state: S
  mutations: M
  actions: A
  getters: { [key in keyof G]: ReturnType<G[key]> }
}

class VuexStore<S, M, A, G extends GettersOption<S>> {

  option = null

  constructor(options: any = {}) {
    this.option = options
  }

  state<O>(state: O) {
    return new VuexStore<O, M, A, GettersOption<O>>(Object.assign(this.option, { state }))
  }

  getters<O extends { [key: string]: (state: S) => any }>(getters: O) {
    return new VuexStore<S, M, A, O>(Object.assign(this.option, { getters }))
  }

  create(): Store<S, M, A, G> {
    return new Vuex.Store(this.option) as any
  }
}

const store = (new VuexStore)
  .state({
    count: 0
  })
  .getters({
    plus: state => state.count + 1,
    string: state => state.count.toString()
  })
  .create()