Vue.js and Vuex - best practices for managing your state

vue.md

Vue.js and Vuex - best practices for managing your state

Modifying state object

Example

If you have to extend an existing object with additional property, always prefer Vue.set() over Object.assign() (or spread operator).

Example below explains implications for different implementations.

const store = new Vuex.Store({
  state: {
    user: {
      id: 1
    }
  },
  getters: {
    getUserId: state => state.user.id,
    getUserName: state => state.user.name
  },
  mutations: {
    setUserName (state, name) {
      // 1st solution:
      // it won't trigger getters at all, more details:
      // https://vuejs.org/v2/guide/reactivity.html#Change-Detection-Caveats
      state.user.name = name

      // 2nd solution:
      // same as "state.user = Object.assign({}, state.user, { name })"
      // it will trigger both getters every time when you call this mutation
      state.user = { ...state.user, name }

      // 3rd solution:
      // it will trigger both getters when you call this mutation for the first time,
      // but if you call it the next time only getUserName() will be triggered
      // Vue.set() will check if property already exists before re-assigning the entire object
      Vue.set(state.user, 'name', name)
    }  
  }
})

Ideally, try to initialize your state with all desired fields upfront, so in the example above state should be declared in the following way:

state: {
  user: {
    id: 1,
    name: null
  }
}

Summary

Be aware that adding a new property to an existing state object can have a significant impact on your application performance. It will trigger all getters based on that object (and potentially computed properties declared inside your componets).

When your application gets bigger over time and your state becomes more complex, try to use modules for better data encapsulation. So even if you have to add a new property at least it will have an impact only on a single module.

Same rules apply to nested objects and their properties, so prefer flat structure when you are designing your store schema.

Modifying state array

Example

If you have to add a new object to an existing array, always define all potential properties of the object upfront even if you do not know their values at the time.

Check the example below for more details.

const store = new Vuex.Store({
  state: {
    users: []
  },
  getters: {
    getUsersNames: state => {
      return state.users.map(user => user.name)
    }
  },
  mutations: {
    addUser (state, name) {
      // 1st solution:
      // it will work as expected and trigger getUsersNames()
      state.users.push({name})

      // 2nd solution
      // even though we are recreating the entire array,
      // it will behave in the same way as first solution
      // more details: https://vuejs.org/v2/guide/list.html#Replacing-an-Array
      state.users = [...state.users, {name}]
    },
    updateUserAvatar (state, {index, avatar}) {
      // 1st solution:
      // it will properly update an array item, but also it will trigger getUsersNames()
      Vue.set(state.users[index], 'avatar', avatar)

      // 2nd solution:
      // it's going to work only if we modify addUser() function and include avatar property there:
      // "state.users.push({name, avatar: null})"
      // the benefit of this approach is that getUsersNames() won't be triggered
      state.users[index].avatar = avatar
    }
  }
})

Summary

Be aware that adding a new item to an existing state array will always trigger all getters (and computed properties) which are based on that array. Same will happen if you remove the item.

When you add or remove items from an array it's okay to recreate the array entirely - feel free to use latest JavaScript features like spread operator or simply call array's mutation methods like push().

Different rules apply when you update existing object inside an array. First of all, declare all object properties (even with null values) before you add it to the array, they will become reactive properties observed by Vue. Avoid adding new properties to the object, it will always trigger all getters that are based on the array. You should modify object properites directly (for example state.users[0].name = "Test") and avoid recreating the entire array for updates.

Could anyone say something about this method of update of an existing item in an array for Vuex. It seems to be working just fine.

const store = new Vuex.Store({
  state: {
    users: []
  },
  mutations: {
     UPDATE_USER (state, editedUser) {
         // find doesn't create a new object, it returns an existing one from users array and we can modify it
         const oldUser = state.users.find( user => user.id === editedUser.id );
         if (oldUser) {
            // not creating a new object but modifying old object here
            Object.assign(oldUser, editedUser)
         }
     },
     ADD_USER (state, user) {
         state.users.push(user);
     },
  }
})

In UPDATE_USER new fields defined in editedUser will be created in old user object from users array, old fields are updated with a new value if old fields of old user object were defined in editedUser and it's totally reactive. I would like to know caveats though.

@Goloburda @jdeeline just a note. While your approach will work in a simple case if you make the case harder like let's say we now have a modal window for editing users and your modal will get a user data like that:

... 

<li v-for="user in users" @click="openModal(user)"> {user.name} </li>
<Modal :user="editUser" :show="showModal" />
...

data: {
    editUser: null,
    showModal: false,
}
methods: {
    openModal (user) {
      this.editUser = user;
      this.showModal = true;
    }
}

After you update user in Vuex store its updated version will not be seen in modal because you replaced that object in Vuex store with a new one and editUser will not be updated, it will still contain the old object.

As workaround you can avoid replacing the entire object and just change each of its properties. Or you can instead of passing entire object in Modal component just pass let's say user.id and then add a computed field (and pass it in the modal window as well) which will search for that user via its user.id

You may need to fix your example. And this is more like basic usage than best practices. It is clean though.

• You can't pass third parameter on mutations/actions.

updateUserAvatar (state, index, avatar)

• Getters without a formatting/filtering are waste of memory. You can directly access state.

getUserId: state => state.user.id,
getUserName: state => state.user.name

I tried the code for the array state, without luck within my Vue / vuex project. I get an error on the return of the getUsersNames => "Property 'name' does not exist on type 'never'"

And an error on the line "state.users.push({name})" => "(property) name: any
Type 'any' is not assignable to type 'never'"

Is the example incomplete, causing this issues at my project, or do I need to change settings to make it work?

Any help is appreciated.

I tried the code for the array state, without luck within my Vue / vuex project. I get an error on the return of the getUsersNames => "Property 'name' does not exist on type 'never'"

And an error on the line "state.users.push({name})" => "(property) name: any
Type 'any' is not assignable to type 'never'"

Hi,

1. did you try to add some data into the state manually?

state: { users: [{ id: 1, name: 'some name' }] }

2. Are you using TypeScript in your project?

I tried the code for the array state, without luck within my Vue / vuex project. I get an error on the return of the getUsersNames => "Property 'name' does not exist on type 'never'"
And an error on the line "state.users.push({name})" => "(property) name: any
Type 'any' is not assignable to type 'never'"

Hi,

1. did you try to add some data into the state manually?

state: { users: [{ id: 1, name: 'some name' }] }

1. Are you using TypeScript in your project?

1. When adding data manually this works okay, however the data should contain openLayers layers and I can't generate it within the stores "constructor" for the array. So I will add the data later was my thought. Is this a wrong idea?

2. I am using typescript, how does this effect the problem?

Is this somehow

1. When adding data manually this works okay, however the data should contain openLayers layers and I can't generate it within the stores "constructor" for the array. So I will add the data later was my thought. Is this a wrong idea?
2. I am using typescript, how does this effect the problem?

Is this somehow

1. If you've got JSON file with openLayers/mapLayers and are using Vuex, you could import your data, for instance, with axios and save it to the store with a mutation function like it's shown in this post:
   https://stackoverflow.com/questions/56075612/how-do-i-use-json-data-with-vuex-store-no-webpack
2. You've got type mismatch error (Type 'any' is not assignable to type 'never') in your first comment. Typescript itself adds additional overhead to your projects and complicates understanding / learning, especially for beginners. If you want to do it properly, you'd need to write your own Vuex types/interfaces for the store according to the structure of the data you're working with. Then you'd need to apply these types to getters, actions and mutations. It's probably a good idea to start with modules, as it's shown in this video.
   However, to inculde Vuex types there are lots of different approaches (see their code), each of which covers some percentage of the Vuex functionality, including the vuex-module-decorator/vue-property-decorator, which still tends to be the "cleanest" one.
   If you're just starting out I wouldn't recommend to use TypeScript within a Vue/Vuex (pet) project at all, unless you know what you're doing, or it's a big project with lots of developers, or an existing codebase with some strict predefined guidelines.

Good luck!

@galakhov:
Many thanks, your responses helped me into the correct directions, and putting things in the correct perspective. I thought typescript would help me get things correctly structured, but probably I can better ignore this (for now).

Thank you for this document. I suggest only a small correction: change 'Modyfing' instances to 'Modifying'. Cheers!

Thanks for the awesome gist!

Hi, thanks for the gist which is very helpful. I am new to Vue and Vuex; got a question posted at https://stackoverflow.com/questions/69684791/nested-components-and-states-in-vue-with-vuex
Would you please take a look?
I am basically not sure how to handle state object having proper which is of type array, and such a property can have dynamic number of items depending on other state triggered from other component.