Detailed explanation of Mutations modification status operation in Vuex

The previous article was about reading state, and this article is about modifying state. That is, how to operate Mutations.

1. $store.commit( )

Vuex provides the commit method to modify the status

1.store.js file

const mutations={
  add(state){
    state.count++
  },
  reduce(state){
    state.count--
  }
}

2. Modification method on button

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2. Pass value

The simplest operation to modify the state. In actual projects, we often need to pass values ​​when modifying the state. For example, in the above example, we only add 1 each time, but now we need to add the values ​​passed. In fact, we only need to add another parameter to Mutations and pass it when committing. Let’s look at the specific code:

1.store.js

const mutations={
  add(state,n){
    state.count+=n
  },
  reduce(state){
    state.count--
  }
}

2. Modify the parameters passed by the commit() method of the button. We pass 10, which means adding 10 each time.

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3. Template acquisition method of Mutations

We don’t like to see it in actual development either When a method like $store.commit() appears, we hope to call it the same way as the method in the template.

For example: @click="reduce" is the same as not referencing the vuex plug-in.

1. Use import to introduce our mapMutations in the template count.vue:

import { mapState,mapMutations } from 'vuex'

2 .Add the methods attribute in the <script> tag of the template, and add mapMutations</script>

 methods:mapMutations([
    'add','reduce'
]),

3. Use our reduce or add method directly in the template

-

Note: Encapsulate $store.commit

  reduce: function () {
   this.$store.commit('add', 10) // html标签是可以不写this
  }

Supplementary knowledge:vuex mutations parameter passing

The next step is to explain the parameter passing of mutations

Add student examples

The first type of passing Parameter method

<template>
 <p>
 <h3 id="这是mutations传参测试">-------------------这是mutations传参测试-------------------</h3>
 <p>
  {{this.$store.state.students}}//将已经有的学生渲染在这儿
  <p>
  <button @click="addstu">点击添加</button>//绑定添加事件
  </p>
 </p>
 </p>
</template>

<script>
export default {
 methods: {
  addstu () {
   const newstu = {
   id: 5,
   name: &#39;张国荣&#39;,
   age: 44
   }//定死一个要添加的学生，这就是要传给mutations的参数
   this.$store.commit(&#39;addStudent&#39;, newstu)
   //调用commit方法，更新state的数据，
   //第一个参数是mutations里面的方法名，
   //第二个参数是传给mutaitons里面addstudent方法的一个参数，
   //也就是要新加入的学生
  }
 }
}
</script>

Receive this parameter in vuex.store

const store = new Vuex.Store({
// 定义的公共变量
  state: {
   count: 1,
   students: [
    {
     id: 1,
     name: 'dx',
     age: 18
    },
    {
     id: 2,
     name: 'yx',
     age: 18
    },
    {
     id: 3,
     name: 'ym',
     age: 32
    },
    {
     id: 4,
     name: '刘亦菲',
     age: 30
    }
   ]
  },
 // state中的变量只能在mutations中通过方法修改
  mutations: {
   changeCount: function (state) {
   state.count++
   console.log('改变了count')
   },
   addStudent (state, stu) {
   state.students.push(stu)
   }//通过这种方式，接收来自组件传过来的新加入的学生
  },
  actions: {
  },
  getters: {
  }
})

The second method of passing parameters

The component passes the parameter to vuex Passing parameters

addstu () {
   const newstu = {
   id: 5,
   name: '张国荣',
   age: 44
   }
   this.$store.commit({
   type: 'addStudent',
   newstu: newstu
   })//原先是传入两个参数，现在直接传入一个对象
   //type就是需要调用的mutations里面的方法
   //newstu就是要求接收的对象，也就是新加入的学生
  }

vuex receives component passing parameters

mutations: {
   addStudent (state, playload) {
   state.students.push(playload.newstu)
   }
  },

It should be noted that the second parameter received by addstudent is a complete object, so the use of parameters is slightly different

Related learning recommendations: javascript video tutorial

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