[Typescript] 113. Hard - Pinia

Create a type-level function whose types is similar to Pinia library. You don't need to implement function actually, just adding types.

Overview

This function receive only one parameter whose type is an object. The object contains 4 properties:

• id - just a string (required)
• state - a function which will return an object as store's state (required)
• getters - an object with methods which is similar to Vue's computed values or Vuex's getters, and details are below (optional)
• actions - an object with methods which can do side effects and mutate state, and details are below (optional)

Getters

When you define a store like this:

const store = defineStore({
  // ...other required fields
  getters: {
    getSomething() {
      return 'xxx'
    }
  }
})

And you should use it like this:

store.getSomething

instead of:

store.getSomething()  // error

Additionally, getters can access state and/or other getters via this, but state is read-only.

Actions

When you define a store like this:

const store = defineStore({
  // ...other required fields
  actions: {
    doSideEffect() {
      this.xxx = 'xxx'
      return 'ok'
    }
  }
})

Using it is just to call it:

const returnValue = store.doSideEffect()

Actions can return any value or return nothing, and it can receive any number of parameters with different types. Parameters types and return type can't be lost, which means type-checking must be available at call side.

State can be accessed and mutated via this. Getters can be accessed via this but they're read-only.

/* _____________ Your Code Here _____________ */

type GetRes<T> = T extends (...args: any[]) => infer R ? R : never
declare function defineStore<State, Getters, Actions, _Getters = {
  readonly [P in keyof Getters]: GetRes<Getters[P]>
}>(store: {
  id: string,
  state: (this: void) => State,
  getters?: Getters & ThisType<_Getters & Readonly<State>>
  actions?: Actions & ThisType<State & _Getters & Actions>
}): State & _Getters & Actions;

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

const store = defineStore({
  id: '',
  state: () => ({
    num: 0,
    str: '',
  }),
  getters: {
    stringifiedNum() {
      // @ts-expect-error
      this.num += 1

      return this.num.toString()
    },
    parsedNum() {
      return parseInt(this.stringifiedNum)
    },
  },
  actions: {
    init() {
      this.reset()
      this.increment()
    },
    increment(step = 1) {
      this.num += step
    },
    reset() {
      this.num = 0

      // @ts-expect-error
      this.parsedNum = 0

      return true
    },
    setNum(value: number) {
      this.num = value
    },
  },
})

// @ts-expect-error
store.nopeStateProp
// @ts-expect-error
store.nopeGetter
// @ts-expect-error
store.stringifiedNum()
store.init()
// @ts-expect-error
store.init(0)
store.increment()
store.increment(2)
// @ts-expect-error
store.setNum()
// @ts-expect-error
store.setNum('3')
store.setNum(3)
const r = store.reset()

type _tests = [
  Expect<Equal<typeof store.num, number>>,
  Expect<Equal<typeof store.str, string>>,
  Expect<Equal<typeof store.stringifiedNum, string>>,
  Expect<Equal<typeof store.parsedNum, number>>,
  Expect<Equal<typeof r, true>>,
]