Vue.js – Accessing getters within Vuex mutations

vue.jsvuejs2vuex

Within a Vuex store mutation, is it possible to access a getter? Consider the below example.

new Vuex.Store({
    state: {
        question: 'Is it possible to access getters within a Vuex mutation?'
    },
    mutations: {
        askQuestion(state) {
            // TODO: Get question from getter here
            let question = '';

            if (question) {
                // ...
            }
        }
    },
    getters: {
        getQuestion: (state) => {
            return state.question;
        }
    }
});

Of course the example doesn't make much sense, because I could just access the question property directly on the state object within the mutation, but I hope you see what I am trying to do. That is, conditionally manipulating state.

Within the mutation, this is undefined and the state parameter gives access to the state object, and not the rest of the store.

The documentation on mutations doesn't mention anything about doing this.

My guess would be that it's not possible, unless I missed something? I guess the alternative would be to either perform this logic outside of the store (resulting in code duplication) or implementing an action that does this, because actions have access to the entire store context. I'm pretty sure that it's a better approach, that is to keep the mutation focused on what it's actually supposed to do; mutate the state. That's probably what I'll end up doing, but I'm just curious if accessing a getter within a mutation is even possible?

Best Answer

Vuex store mutation methods do not provide direct access to getters.

This is probably bad practice*, but you could pass a reference to getters when committing a mutation like so:

actions: {
  fooAction({commit, getters}, data) {
    commit('FOO_MUTATION', {data, getters})
  }
},
mutations: {
  FOO_MUTATION(state, {data, getters}) {
    console.log(getters);
  }
}

* It is best practice to keep mutations a simple as possible, only directly affecting the Vuex state. This makes it easier to reason about state changes without having to think about any side effects. Now, if you follow best practices for vuex getters, they should not have any side effects in the first place. But, any logic that needs to reference getters can run in an action, which has read access to getters and state. Then the output of that logic can be passed to the mutation. So, you can pass the reference to the getters object to the mutation, but there's no need to and it muddies the waters.

Related Solutions

Vue.js – Vuex Action vs Mutations

Question 1: Why the Vuejs developers decided to do it this way?

Answer:

When your application becomes large, and when there are multiple developers working on this project, you will find the "state manage" (especially the "global state"), will become increasingly more complicated.
The vuex way (just like Redux in react.js) offers a new mechanism to manage state, keep state, and "save and trackable" (that means every action which modifies state can be tracked by debug tool:vue-devtools)

Question 2: What's the difference between "action" and "mutation"?

Let's see the official explanation first:

Mutations:

Vuex mutations are essentially events: each mutation has a name and a handler.

import Vuex from 'vuex'

const store = new Vuex.Store({
  state: {
    count: 1
  },
  mutations: {
    INCREMENT (state) {
      // mutate state
      state.count++
    }
  }
})

Actions: Actions are just functions that dispatch mutations.

// the simplest action
function increment ({commit}) {
  commit('INCREMENT')
}

// a action with additional arguments
// with ES2015 argument destructuring
function incrementBy ({ dispatch }, amount) {
  dispatch('INCREMENT', amount)
}

Here is my explanation of the above:

mutation is the only way to modify state
mutation doesn't care about business logic, it just cares about "state"
action is business logic
action can commit more than 1 mutation at a time, it just implements the business logic, it doesn't care about data changing (which manage by mutation)

Vue.js – How to access Vuex module getters and mutations

In Addition to the accepted answer I wanna provide you with a workarround for the getter which is missing in the answer.

Debug the Store
In any case you can call console.log(this.$store) to debug the Store.
If you do so you will see the getters are prefixed with the namespace in their name.

Access namespaced getter
this.$store.getters['yourModuleName/someGetterMethod']

Dispatch namespaced
this.$store.dispatch('yourModuleName/doSomething')

Dispatch namespaced with params
this.$store.getters['yourModuleName/someGetterMethod'](myParam)

Conclusion
The key is to handle the namespace like a file System like Justin explained.

Edit: found a nice library for handling vuex Store
In addition to the basic knowledge I'd like to add this vuex library as a nice addition for working effectivly and fast with the vuex store. https://github.com/davestewart/vuex-pathify .
It looks pretty interesting and cares much of the configuration for you and also allows you to handle 2waybinding directly with vuex.

** Edit: Thanks to the other Answers. Added Dispatching method with params for wholeness.

Best Answer

Related Solutions

Vue.js – Vuex Action vs Mutations

Vue.js – How to access Vuex module getters and mutations

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