there is an introduction on the official website

mapState helper function

when a component needs to acquire multiple states, declaring these states as computational properties can be repetitive and redundant. To solve this problem, we can use the mapState helper function to help us generate calculation properties so that you can press the key

//  Vuex.mapState
import { mapState } from 'vuex'

export default {
  // ...
  computed: mapState({
    // 
    count: state => state.count,

    //  'count'  `state => state.count`
    countAlias: 'count',

    //  `this` 
    countPlusLocalState (state) {
      return state.count + this.localCount
    }
  })
}

mapGetters helper function

mapGetters helper function simply maps getter in store to the local evaluation attribute:

import { mapGetters } from 'vuex'

export default {
  // ...
  computed: {
  //  getter  computed 
    ...mapGetters([
      'doneTodosCount',
      'anotherGetter',
      // ...
    ])
  }
}