Vuex Action vs Mutations

Question

In Vuex, what is the logic of having both "actions" and "mutations?"

I understand the logic of components not being able to modify state (which seems smart), but having both actions and mutations seems like you are writing one function to trigger another function, to then alter state.

What is the difference between "actions" and "mutations," how do they work together, and moreso, I'm curious why the Vuex developers decided to do it this way?

Answer 1

1.From docs:

Actions are similar to mutations, the differences being that:

• Instead of mutating the state, actions commit mutations.
• Actions can contain arbitrary asynchronous operations.

The Actions can contain asynchronous operations, but the mutation can not.

2.We invoke the mutation, we can change the state directly. and we also can in the action to change states by like this:

actions: {
  increment (store) {
    // do whatever ... then change the state
    store.commit('MUTATION_NAME')
  }
}

the Actions is designed for handle more other things, we can do many things in there(we can use asynchronous operations) then change state by dispatch mutation there.

Answer 2

I have been using Vuex professionally for about 3 years, and here is what I think I have figured out about the essential differences between actions and mutations, how you can benefit from using them well together, and how you can make your life harder if you don't use it well.

The main goal of Vuex is to offer a new pattern to control the behaviour of your application: Reactivity. The idea is to offload the orchestration of the state of your application to a specialized object: a store. It conveniently supplies methods to connect your components directly to your store data to be used at their own convenience. This allows your components to focus on their job: defining a template, style, and basic component behaviour to present to your user. Meanwhile, the store handles the heavy data load.

That is not the only advantage of this pattern though. The fact that stores are a single source of data for the entirety of your application offers a great potential for re-usability of this data across many components. This isn't the first pattern that attempts to address this issue of cross-component communication, but where it shines is that it forces you to implement a very safe behaviour in your application by basically forbidding your components to modify the state of this shared data, and force it instead to use "public endpoints" to ask for change.

The basic idea is this:

• The store has an internal state, which should never be directly accessed by components (mapState is effectively banned)
• The store has mutations, which are synchronous modifications to the internal state. A mutation's only job is to modify the state. They should only be called from an action. They should be named to describe things that happened to the state (ORDER_CANCELED, ORDER_CREATED). Keep them short and sweet. You can step through them by using the Vue Devtools browser extension (it's great for debugging too!)
• The store also has actions, which should be async or return a promise. They are the actions that your components will call when they want to modify the state of the application. They should be named with business oriented actions (verbs, i.e. cancelOrder, createOrder). This is where you validate and send your requests. Each action may call different commits at different steps if it is required to change the state.
• Finally, the store has getters, which are what you use to expose your state to your components. Expect them to be heavily used across many components as your application expands. Vuex caches getters heavily to avoid useless computation cycles (as long as you don't add parameters to your getter - try not to use parameters) so don't hesitate to use them extensively. Just make sure you give names that describe as closely as possible what state the application currently is in.

That being said, the magic begins when we start designing our application in this manner. For example:

• We have a component that offers a list of orders to the user with the possibility to delete those orders
• The component has mapped a store getter (deletableOrders), which is an array of objects with ids
• The component has a button on each row of orders, and its click is mapped to a store action (deleteOrder) which passes the order object to it (which, we will remember, comes from the store's list itself)
• The store deleteOrder action does the following:
  • it validates the deletion
  • it stores the order to delete temporarily
  • it commits the ORDER_DELETED mutation with the order
  • it sends the API call to actually delete the order (yes, AFTER modifying the state!)
  • it waits for the call to end (the state is already updated) and on failure, we call the ORDER_DELETE_FAILED mutation with the order we kept earlier.
• The ORDER_DELETED mutation will simply remove the given order from the list of deletable orders (which will update the getter)
• The ORDER_DELETE_FAILED mutation simply puts it back, and modifies the state to notify of the error (another component, error-notification, would be tracking that state to know when to display itself)

In the end, we have a user experience that is deemed as "reactive". From the perspective of our user, the item has been deleted immediately. Most of the time, we expect our endpoints to just work, so this is perfect. When it fails, we still have some control over how our application will react, because we have successfully separated the concern of the state of our front-end application, with the actual data.

You don't always need a store, mind you. If you find that you are writing stores that look like this:

export default {
  state: {
    orders: []
  },
  mutations: {
    ADD_ORDER (state, order) {
       state.orders.push(order)
    },
    DELETE_ORDER (state, orderToDelete) {
       state.orders = state.orders.filter(order => order.id !== orderToDelete.id)
    }
  },
  actions: {
    addOrder ({commit}, order) {
      commit('ADD_ORDER', order)
    },
    deleteOrder ({commit}, order) {
      commit('DELETE_ORDER', order)
    }
  },
  getters: {
    orders: state => state.orders
  }
}

To me it seems you are only using the store as a data store, and are perhaps missing out on the reactivity aspect of it, by not letting it also take control of variables that your application reacts to. Basically, you can and should probably offload some lines of code written in your components to your stores.

Answer 3

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

Answer:

1. When your application becomes large, and when there are multiple developers working on this project, you will find that "state management" (especially the "global state") becomes increasingly more complicated.
2. 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:

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

Answer 4

The main differences between Actions and Mutations:

1. In mutations you can change the state but not it actions.
2. Inside actions you can run asynchronous code but not in mutations.
3. Inside actions you can access getters, state, mutations (committing them), actions (dispatching them) etc in mutations you can access only the state.

Answer 5

I believe that having an understanding of the motivations behind Mutations and Actions allows one to better judge when to use which and how. It also frees the programmer from the burden of uncertainty in situations where the "rules" become fuzzy. After reasoning a bit about their respective purposes, I came to the conclusion that although there may definitely be wrong ways to use Actions and Mutations, I don't think that there's a canonical approach.

Let's first try to understand why we even go through either Mutations or Actions.

Why go through the boilerplate in the first place? Why not change state directly in components?

Strictly speaking you could change the state directly from your components. The state is just a JavaScript object and there's nothing magical that will revert changes that you make to it.

// Yes, you can!
this.$store.state['products'].push(product)

However, by doing this you're scattering your state mutations all over the place. You lose the ability to simply just open a single module housing the state and at a glance see what kind of operations can be applied to it. Having centralized mutations solves this, albeit at the cost of some boilerplate.

// so we go from this
this.$store.state['products'].push(product)

// to this
this.$store.commit('addProduct', {product})

...
// and in store
addProduct(state, {product}){
    state.products.push(product)
}
...

I think if you replace something short with boilerplate you'll want the boilerplate to also be small. I therefore presume that mutations are meant to be very thin wrappers around native operations on the state, with almost no business logic. In other words, mutations are meant to be mostly used like setters.

Now that you've centralized your mutations you have a better overview of your state changes and since your tooling (vue-devtools) is also aware of that location it makes debugging easier. It's also worth keeping in mind that many Vuex's plugins don't watch the state directly to track changes, they rather rely on mutations for that. "Out of bound" changes to the state are thus invisible to them.

So mutations, actions what's the difference anyway?

Actions, like mutations, also reside in the store's module and can receive the state object. Which implies that they could also mutate it directly. So what's the point of having both? If we reason that mutations have to be kept small and simple, it implies that we need an alternative means to house more elaborate business logic. Actions are the means to do this. And since as we have established earlier, vue-devtools and plugins are aware of changes through Mutations, to stay consistent we should keep using Mutations from our actions. Furthermore, since actions are meant to be all encompassing and that the logic they encapsulate may be asynchronous, it makes sense that Actions would also simply made asynchronous from the start.

It's often emphasized that actions can be asynchronous, whereas mutations are typically not. You may decide to see the distinction as an indication that mutations should be used for anything synchronous (and actions for anything asynchronous); however, you'd run into some difficulties if for instance you needed to commit more than one mutations (synchronously), or if you needed to work with a Getter from your mutations, as mutation functions receive neither Getters nor Mutations as arguments...

...which leads to an interesting question.

Why don't Mutations receive Getters?

I haven't found a satisfactory answer to this question, yet. I have seen some explanation by the core team that I found moot at best. If I summarize their usage, Getters are meant to be computed (and often cached) extensions to the state. In other words, they're basically still the state, albeit that requires some upfront computation and they're normally read-only. That's at least how they're encouraged to be used.

Thus, preventing Mutations from directly accessing Getters means that one of three things is now necessary, if we need to access from the former some functionality offered by the latter: (1) either the state computations provided by the Getter is duplicated somewhere that is accessible to the Mutation (bad smell), or (2) the computed value (or the relevant Getter itself) is passed down as an explicit argument to the Mutation (funky), or (3) the Getter's logic itself is duplicated directly within the Mutation, without the added benefit of caching as provided by the Getter (stench).

The following is an example of (2), which in most scenarios that I have encountered seems the "least bad" option.

state:{
    shoppingCart: {
        products: []
    }
},

getters:{
    hasProduct(state){
        return function(product) { ... }
    }
}

actions: {
    addProduct({state, getters, commit, dispatch}, {product}){

        // all kinds of business logic goes here

        // then pull out some computed state
        const hasProduct = getters.hasProduct(product)
        // and pass it to the mutation
        commit('addProduct', {product, hasProduct})
    }
}

mutations: {
    addProduct(state, {product, hasProduct}){ 
        if (hasProduct){
            // mutate the state one way
        } else {
            // mutate the state another way 
        }
    }
}

To me, the above seems not only a bit convoluted, but also somewhat "leaky", since some of the code present in the Action is clearly oozing from the Mutation's internal logic.

In my opinion, this is an indication of a compromise. I believe that allowing Mutations to automatically receive Getters presents some challenges. It can be either to the design of Vuex itself, or the tooling (vue-devtools et al), or to maintain some backward compatibility, or some combination of all the stated possibilities.

What I don't believe is that passing Getters to your Mutations yourself is necessarily a sign that you're doing something wrong. I see it as simply "patching" one of the framework's shortcomings.

Answer 6

It might seem unnecessary to have an extra layer of actions just to call the mutations, for example:

const actions = {
  logout: ({ commit }) => {
    commit("setToken", null);
  }
};

const mutations = {
  setToken: (state, token) => {
    state.token = token;
  }
};

So if calling actions calls logout, why not call the mutation itself?

The entire idea of an action is to call multiple mutations from inside one action or make an Ajax request or any kind of asynchronous logic you can imagine.

We might eventually have actions that make multiple network requests and eventually call many different mutations.

So we try to stuff as much complexity from our Vuex.Store() as possible in our actions and this leaves our mutations, state and getters cleaner and straightforward and falls in line with the kind of modularity that makes libraries like Vue and React popular.

Answer 7

Mutations:

Can update the state. (Having the Authorization to change the state).

Actions:

Actions are used to tell "which mutation should be triggered"

In Redux Way

Mutations are Reducers
Actions are Actions

Why Both ??

When the application growing , coding and lines will be increasing , That time you have to handle the logic in Actions not in the mutations because mutations are the only authority to change the state, it should be clean as possible.

Answer 8

This confused me too so I made a simple demo.

component.vue

<template>
    <div id="app">
        <h6>Logging with Action vs Mutation</h6>
        <p>{{count}}</p>
        <p>
            <button @click="mutateCountWithAsyncDelay()">Mutate Count directly with delay</button>
        </p>
        <p>
            <button @click="updateCountViaAsyncAction()">Update Count via action, but with delay</button>
        </p>
        <p>Note that when the mutation handles the asynchronous action, the "log" in console is broken.</p>
        <p>When mutations are separated to only update data while the action handles the asynchronous business
            logic, the log works the log works</p>
    </div>
</template>

<script>

        export default {
                name: 'app',

                methods: {

                        //WRONG
                        mutateCountWithAsyncDelay(){
                                this.$store.commit('mutateCountWithAsyncDelay');
                        },

                        //RIGHT
                        updateCountViaAsyncAction(){
                                this.$store.dispatch('updateCountAsync')
                        }
                },

                computed: {
                        count: function(){
                                return this.$store.state.count;
                        },
                }

        }
</script>

store.js

import 'es6-promise/auto'
import Vuex from 'vuex'
import Vue from 'vue';

Vue.use(Vuex);

const myStore = new Vuex.Store({
    state: {
        count: 0,
    },
    mutations: {

        //The WRONG way
        mutateCountWithAsyncDelay (state) {
            var log1;
            var log2;

            //Capture Before Value
            log1 = state.count;

            //Simulate delay from a fetch or something
            setTimeout(() => {
                state.count++
            }, 1000);

            //Capture After Value
            log2 = state.count;

            //Async in mutation screws up the log
            console.log(`Starting Count: ${log1}`); //NRHG
            console.log(`Ending Count: ${log2}`); //NRHG
        },

        //The RIGHT way
        mutateCount (state) {
            var log1;
            var log2;

            //Capture Before Value
            log1 = state.count;

            //Mutation does nothing but update data
            state.count++;

            //Capture After Value
            log2 = state.count;

            //Changes logged correctly
            console.log(`Starting Count: ${log1}`); //NRHG
            console.log(`Ending Count: ${log2}`); //NRHG
        }
    },

    actions: {

        //This action performs its async work then commits the RIGHT mutation
        updateCountAsync(context){
            setTimeout(() => {
                context.commit('mutateCount');
            }, 1000);
        }
    },
});

export default myStore;

After researching this, the conclusion I came to is that mutations are a convention focused only on changing data to better separate concerns and improve logging before and after the updated data. Whereas actions are a layer of abstraction that handles the higher level logic and then calls the mutations appropriately

Answer 9

Because there’s no state without mutations! When commited — a piece of logic, that changes the state in a foreseeable manner, is executed. Mutations are the only way to set or change the state (so there’s no direct changes!), and furthermore — they must be synchronous. This solution drives a very important functionality: mutations are logging into devtools. And that provides you with a great readability and predictability!

One more thing — actions. As it’s been said — actions commit mutations. So they do not change the store, and there’s no need for these to be synchronous. But, they can manage an extra piece of asynchronous logic!

Answer 10

Disclaimer - I've only just started using vuejs so this is just me extrapolating the design intent.

Time machine debugging uses snapshots of the state, and shows a timeline of actions and mutations. In theory we could have had just actions alongside a recording of state setters and getters to synchronously describe mutation. But then:

• We would have impure inputs (async results) which caused the setters and getters. This would be hard to follow logically and different async setters and getters may surprisingly interact. That can still happen with mutations transactions but then we can say the transaction needs to be improved as opposed to it being a race condition in the actions. Anonymous mutations inside an action could more easily resurface these kinds of bugs because async programming is fragile and difficult.
• The transaction log would be hard to read because there would be no name for the state changes. It would be much more code-like and less English, missing the logical groupings of mutations.
• It might be trickier and less performant to instrument recording any mutation on a data object, as opposed to now where there are synchronously defined diff points - before and after mutation function call. I'm not sure how big of a problem that is.

Compare the following transaction log with named mutations.

Action: FetchNewsStories
Mutation: SetFetchingNewsStories
Action: FetchNewsStories [continuation]
Mutation: DoneFetchingNewsStories([...])

With a transaction log that has no named mutations:

Action: FetchNewsStories
Mutation: state.isFetching = true;
Action: FetchNewsStories [continuation]
Mutation: state.isFetching = false;
Mutation: state.listOfStories = [...]

I hope you can extrapolate from that example the potential added complexity in async and anonymous mutation inside actions.

https://vuex.vuejs.org/en/mutations.html

Now imagine we are debugging the app and looking at the devtool's mutation logs. For every mutation logged, the devtool will need to capture a "before" and "after" snapshots of the state. However, the asynchronous callback inside the example mutation above makes that impossible: the callback is not called yet when the mutation is committed, and there's no way for the devtool to know when the callback will actually be called - any state mutation performed in the callback is essentially un-trackable!

Answer 11

According to the docs

Actions are similar to mutations, the differences being that:

• Instead of mutating the state, actions commit mutations.
• Actions can contain arbitrary asynchronous operations.

Consider the following snippet.

const store = new Vuex.Store({
  state: {
    count: 0
  },
  mutations: {
    increment (state) {
      state.count++               //Mutating the state. Must be synchronous
    }
  },
  actions: {
    increment (context) {
      context.commit('increment') //Committing the mutations. Can be asynchronous.
    }
  }
})

Action handlers(increment) receive a context object which exposes the same set of methods/properties on the store instance, so you can call context.commit to commit a mutation, or access the state and getters via context.state and context.getters

Answer 12

I think the TLDR answer is that Mutations are meant to be synchronous/transactional. So if you need to run an Ajax call, or do any other asynchronous code, you need to do that in an Action, and then commit a mutation after, to set the new state.

Answer 13

Mutations are synchronous, whereas actions can be asynchronous.

To put it in another way: you don't need actions if your operations are synchronous, otherwise implement them.