# 总结

我们先看一个有无使用mapXXX的demo

没使用

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <script src="https://cdn.jsdelivr.net/npm/vue"></script>
  <script src="https://unpkg.com/vuex@2.0.0"></script>
</head>
<body>
  <div id="app">
    <Button @click="handleAdd">添加</Button>
    <ul>
      <li v-for="num of nums" :key="num">
        {{num}}
      </li>
    </ul>
    <h5>最大的: {{ maxNum }}</h5>
  </div>
  <script>
    store = new Vuex.Store({
      state: {
        nums: []
      },
      mutations: {
        add(state, num) {
          state.nums.push(num);
        }
      },
      getters: {
        maxNum(state) {
          return Math.max(...state.nums);
        }
      }
    })

    const { mapState, mapGetters, mapMutations } = Vuex;

    new Vue({
      el: "#app",
      store,
      computed: {
        nums() {
          return this.$store.state.nums;
        },
        maxNum() {
          return this.$store.getters.maxNum;
        }
      },
      methods: {
        add(num) {
          return this.$store.mutations.commit('add', num);
        },
        handleAdd() {
          const num = parseInt(Math.random()*100);
          this.add(num);
        }
      }
    })

  </script>
  
</body>
</html>

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使用了

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <script src="https://cdn.jsdelivr.net/npm/vue"></script>
  <script src="https://unpkg.com/vuex@2.0.0"></script>
</head>
<body>
  <div id="app">
    <Button @click="handleAdd">添加</Button>
    <ul>
      <li v-for="num of nums" :key="num">
        {{num}}
      </li>
    </ul>
    <h5>最大的: {{ maxNum }}</h5>
  </div>
  <script>
    store = new Vuex.Store({
      state: {
        nums: []
      },
      mutations: {
        add(state, num) {
          state.nums.push(num);
        }
      },
      getters: {
        maxNum(state) {
          return Math.max(...state.nums);
        }
      }
    })

    const { mapState, mapGetters, mapMutations } = Vuex;

    new Vue({
      el: "#app",
      store,
      computed: {
        ...mapState(['nums']),
        ...mapGetters(['maxNum'])
      },
      methods: {
        ...mapMutations(['add']),
        handleAdd() {
          const num = parseInt(Math.random()*100);
          this.add(num);
        }
      }
    })

  </script>
  
</body>
</html>

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通过以上几个map的实现可以总结出这些map实际上帮我们干了以下几件事儿:

自动创建了一个以数组元素或者对象key的名称的函数
如果有命名空间的，通过命名空间获取对应的module
函数里自动获取this.$store.xxxx,然进行this.$store.xxx的操作

大家从demo中就可以看出，在没有mapXXX时，vue每次使用store中的任何功能时，都需要重复上述至少两个事情，重复的事情最好一次解决，vuex的mapXXX就是解决这个问题的,把这些搬砖的事情统一解决了

← mapActions