Differences b/n mapState, mapGetters, mapActions, mapMutations in Vuex

问题

I have been using vue/vuex for months and I see mapState, mapGetters, mapActions, mapMutations but don't know what they do except for mapState.

This is how I use mapState

// mutations.js 
user: {
   address: {},
   name: '',
   age: ''
}

and in my code I have something like this:

import { mapState } from 'vuex'
export default {
  data: {},

  computed: {
   ...mapState({
    address: state => state.user.address
   })
  }
}

then I can use address anywhere, but I don't know what the others are used for.

can someone give a simple example? thanks

回答1:

None of those mappers are mandatory. Their goal is just to make easy to create computed properties or methods in the components. They are DRY (avoid duplication) at its best.

mapState is a helper that simplifies creating a computed property that reflects the value of a given state.

Similarly:

mapGetters is a helper that simplifies creating a computed property that reflects the value returned by a given getter.
- Note that even method-style getters should be mapped to computed properties.
mapActions is a helper that simplifies creating a method that would be equivalent as calling dispatch on an action.
mapMutations is a helper that simplifies creating a method that would be equivalent as calling commit on an mutation.

Since code helps, the demo below shows examples of using all those mappers, and their equivalent without mappers. Their behavior is exactly the same. The mappers just allow you to write with less code (consider that this will be repeated in many, many components of your app).

const store = new Vuex.Store({
  strict: true,
  state: {name: "John"},
  mutations: {
  	changeName(state, data) {
    	state.name = data
    }
  },
  actions: {
    fetchRandomName({ commit }) {
      let randomId = Math.floor(Math.random() * 12) + 1  ;
      axios.get("https://reqres.in/api/users/" + randomId).then(response => {
        commit('changeName', response.data.data.first_name)
      })
    }
  },
  getters: {
    getName: state => state.name,
    getTransformedName: (state) => (upperOrLower) => {
      return upperOrLower ? state.name.toUpperCase() : state.name.toLowerCase()
    }
  }
});
new Vue({
  store,
  el: '#app',
  data: { newName: 'Bob' },
  computed: {
    ...Vuex.mapState(['name']),
    nameNoMapper() { return this.$store.state.name },
    ...Vuex.mapGetters(['getName', 'getTransformedName']),
    getNameNoMapper() { return this.$store.getters.getName },
    getTransformedNameNoMapper() { return this.$store.getters.getTransformedName }
  },
  methods: {
    ...Vuex.mapActions(['fetchRandomName']),
    ...Vuex.mapMutations(['changeName']),
    fetchRandomNameNoMapper() { this.$store.dispatch('fetchRandomName') },
    changeNameNoMapper(newName) { this.$store.commit('changeName', newName) },
  }
})

table, tr, td {
  font-family: monospace;
  border: 1px solid black;
  border-collapse: collapse;
}

<script src="https://unpkg.com/vue"></script>
<script src="https://unpkg.com/vuex"></script>
<script src="https://unpkg.com/axios@0.18.0/dist/axios.min.js"></script>

<div id="app">
  <table>
    <tr>
      <td style="width: 250px">With Mappers</td>
      <td style="width: 310px">Without Mappers</td>
    </tr>
    <tr>
      <td>
        name: {{ name }}<br>
        getName: {{ getName }}<br>
        getTransformedName(true): {{ getTransformedName(true) }}<br>
        getTransformedName(false): {{ getTransformedName(false) }}
      </td>
      <td>
        nameNoMapper: {{ nameNoMapper }}<br>
        getNameNoMapper: {{ getNameNoMapper }}<br>
        getTransformedNameNoMapper(true): {{ getTransformedNameNoMapper(true) }}<br>
        getTransformedNameNoMapper(false): {{ getTransformedNameNoMapper(false) }}
      </td>
    </tr>
  </table>
  <hr>
  <button @click="fetchRandomName">ACTION: fetchRandomName</button> - <button @click="fetchRandomNameNoMapper">ACTION: fetchRandomNameNoMapper</button><br>
  <hr>
  <input v-model="newName"><button @click="changeName(newName)">MUTATION: changeName</button><button @click="changeNameNoMapper(newName)">MUTATION: changeNameNoMapper</button>
</div>

来源：https://stackoverflow.com/questions/49696542/differences-b-n-mapstate-mapgetters-mapactions-mapmutations-in-vuex

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