How to watch store values from vuex?

Let's say, for example, that you have a basket of fruits, and each time you add or remove a fruit from the basket, you want to (1) display info about fruit count, but you also (2) want to be notified of the count of the fruits in some fancy fashion...

fruit-count-component.vue

<template> <!-- We meet our first objective (1) by simply --> <!-- binding to the count property. --> <p>Fruits: {{ count }}</p> </template> <script> import basket from '../resources/fruit-basket' export default () { computed: { count () { return basket.state.fruits.length // Or return basket.getters.fruitsCount // (depends on your design decisions). } }, watch: { count (newCount, oldCount) { // Our fancy notification (2). console.log(`We have ${newCount} fruits now, yay!`) } } } </script> 

Please note, that the name of the function in the watch object, must match the name of the function in the computed object. In the example above the name is count.

New and old values of a watched property will be passed into watch callback (the count function) as parameters.

The basket store could look like this:

fruit-basket.js

import Vue from 'vue' import Vuex from 'vuex' Vue.use(Vuex) const basket = new Vuex.Store({ state: { fruits: [] }, getters: { fruitsCount (state) { return state.fruits.length } } // Obviously you would need some mutations and actions, // but to make example cleaner I'll skip this part. }) export default basket 

You can read more in the following resources:

• Computed properties and watchers
• API docs: computed
• API docs: watch

It's as simple as:

watch: { '$store.state.drawer': function() { console.log(this.$store.state.drawer) } } 

If the store is in a module, use:

'$store.state.myModule.drawer' 

For nested files, use:

'$store.state.fileOne.fileTwo.myModule.drawer' 

As mentioned above it is not good idea to watch changes directly in store

But in some very rare cases it may be useful for someone, so i will leave this answer. For others cases, please see @gabriel-robert answer

You can do this through state.$watch. Add this in your created (or where u need this to be executed) method in component

this.$store.watch( function (state) { return state.my_state; }, function () { //do something on data change }, { deep: true //add this if u need to watch object properties change etc. } ); 

More details: https://vuex.vuejs.org/api/#watch

I think the asker wants to use watch with Vuex.

this.$store.watch( (state)=>{ return this.$store.getters.your_getter }, (val)=>{ //something changed do something }, { deep:true } ); 

This is for all the people that cannot solve their problem with getters and actually really need a watcher, e.g. to talk to non-vue third party stuff (see Vue Watchers on when to use watchers).

Vue component's watchers and computed values both also work on computed values. So it's no different with vuex:

import { mapState } from 'vuex'; export default { computed: { ...mapState(['somestate']), someComputedLocalState() { // is triggered whenever the store state changes return this.somestate + ' works too'; } }, watch: { somestate(val, oldVal) { // is triggered whenever the store state changes console.log('do stuff', val, oldVal); } } } 

if it's only about combining local and global state, the mapState's doc also provides an example:

computed: { ...mapState({ // to access local state with `this`, a normal function must be used countPlusLocalState (state) { return state.count + this.localCount } } }) 

I tried literally everything to get this working.

Theory

I found that for some reason, changes to objects from $store don't necessarily trigger a .watch method. My workaround was to

• Store
  • Create a complex data set which should but doesn't propagate changes to a Component
  • Create an incrementing counter in the state to act as a flag, which does propagate changes to a Component when watched
  • Create a method in $store.mutators to alter the complex dataset and increment the counter flag
• Component
  • Watch for changes in the $store.state flag. When change is detected, update locally relevant reactive changes from the $store.state complex data set
  • Make changes to the $store.state's dataset using our $store.mutators method

Implementation

This is implemented something like this:

Store

let store = Vuex.Store({ state: { counter: 0, data: { someKey: 0 } }, mutations: { updateSomeKey(state, value) { update the state.data.someKey = value; state.counter++; } } }); 

Component

 data: { dataFromStoreDataSomeKey: null, someLocalValue: 1 }, watch: { '$store.state.counter': { immediate: true, handler() { // update locally relevant data this.someLocalValue = this.$store.state.data.someKey; } } }, methods: { updateSomeKeyInStore() { this.$store.commit('updateSomeKey', someLocalValue); } 

Runnable demo

It's convoluted but basically here we are watching for a flag to change and then updating local data to reflect important changes in an object that's stored in the $state

Vue.config.devtools = false const store = new Vuex.Store({ state: { voteCounter: 0, // changes to objectData trigger a watch when keys are added, // but not when values are modified? votes: { 'people': 0, 'companies': 0, 'total': 0, }, }, mutations: { vote(state, position) { state.votes[position]++; state.voteCounter++; } }, }); app = new Vue({ el: '#app', store: store, data: { votesForPeople: null, votesForCompanies: null, pendingVote: null, }, computed: { totalVotes() { return this.votesForPeople + this.votesForCompanies }, peoplePercent() { if (this.totalVotes > 0) { return 100 * this.votesForPeople / this.totalVotes } else { return 0 } }, companiesPercent() { if (this.totalVotes > 0) { return 100 * this.votesForCompanies / this.totalVotes } else { return 0 } }, }, watch: { '$store.state.voteCounter': { immediate: true, handler() { // clone relevant data locally this.votesForPeople = this.$store.state.votes.people this.votesForCompanies = this.$store.state.votes.companies } } }, methods: { vote(event) { if (this.pendingVote) { this.$store.commit('vote', this.pendingVote) } } } })

<script src="https://cdn.jsdelivr.net/npm/[email protected]"></script> <script src="https://unpkg.com/[email protected]/dist/vuex.js"></script> <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css"> <div id="app"> <form @submit.prevent="vote($event)"> <div class="form-check"> <input class="form-check-input" type="radio" name="vote" id="voteCorps" value="companies" v-model="pendingVote" > <label class="form-check-label" for="voteCorps"> Equal rights for companies </label> </div> <div class="form-check"> <input class="form-check-input" type="radio" name="vote" id="votePeople" value="people" v-model="pendingVote" > <label class="form-check-label" for="votePeople"> Equal rights for people </label> </div> <button class="btn btn-primary" :disabled="pendingVote==null" >Vote</button> </form> <div class="progress mt-2" v-if="totalVotes > 0" > <div class="progress-bar" role="progressbar" aria-valuemin="0" :style="'width: ' + peoplePercent + '%'" :aria-aluenow="votesForPeople" :aria-valuemax="totalVotes" >People</div> <div class="progress-bar bg-success" role="progressbar" aria-valuemin="0" :style="'width: ' + companiesPercent + '%'" :aria-valuenow="votesForCompanies" :aria-valuemax="totalVotes" >Companies</div> </div> </div>

if you use typescript then you can :

import { Watch } from "vue-property-decorator"; .. @Watch("$store.state.something") private watchSomething() { // use this.$store.state.something for access ... }

If you simply want to watch a state property and then act within the component accordingly to the changes of that property then see the example below.

In store.js:

export const state = () => ({ isClosed: false }) export const mutations = { closeWindow(state, payload) { state.isClosed = payload } } 

In this scenario, I am creating a boolean state property that I am going to change in different places in the application like so:

this.$store.commit('closeWindow', true) 

Now, if I need to watch that state property in some other component and then change the local property I would write the following in the mounted hook:

mounted() { this.$store.watch( state => state.isClosed, (value) => { if (value) { this.localProperty = 'edit' } } ) } 

Firstly, I am setting a watcher on the state property and then in the callback function I use the value of that property to change the localProperty.

I hope it helps!

Create a Local state of your store variable by watching and setting on value changes. Such that the local variable changes for form-input v-model does not directly mutate the store variable.

data() { return { localState: null }; }, computed: { ...mapGetters({ computedGlobalStateVariable: 'state/globalStateVariable' }) }, watch: { computedGlobalStateVariable: 'setLocalState' }, methods: { setLocalState(value) { this.localState = Object.assign({}, value); } } 

You could also subscribe to the store mutations:

store.subscribe((mutation, state) => { console.log(mutation.type) console.log(mutation.payload) }) 

https://vuex.vuejs.org/api/#subscribe

Inside the component, create a computed function

computed:{ myState:function(){ return this.$store.state.my_state; // return the state value in `my_state` } } 

Now the computed function name can be watched, like

watch:{ myState:function(newVal,oldVal){ // this function will trigger when ever the value of `my_state` changes } } 

The changes made in the vuex state my_state will reflect in the computed function myState and trigger the watch function.

If the state my_state is having nested data, then the handler option will help more

watch:{ myState:{ handler:function(newVal,oldVal){ // this function will trigger when ever the value of `my_state` changes }, deep:true } } 

This will watch all the nested values in the store my_state.

Use your getter in computed then watch it and do what you need

 computed:{ ...mapGetters(["yourGetterName"]) }, watch: { yourGetterName(value) { // Do something you need }, } 

The best way to watch store changes is to use mapGetters as Gabriel said. But there is a case when you can't do it through mapGetters e.g. you want to get something from store using parameter:

getters: { getTodoById: (state, getters) => (id) => { return state.todos.find(todo => todo.id === id) } } 

in that case you can't use mapGetters. You may try to do something like this instead:

computed: { todoById() { return this.$store.getters.getTodoById(this.id) } } 

But unfortunately todoById will be updated only if this.id is changed

If you want you component update in such case use this.$store.watch solution provided by Gong. Or handle your component consciously and update this.id when you need to update todoById.

You can use a combination of Vuex actions, getters, computed properties and watchers to listen to changes on a Vuex state value.

HTML Code:

<div id="app" :style='style'> <input v-model='computedColor' type="text" placeholder='Background Color'> </div> 

JavaScript Code:

'use strict' Vue.use(Vuex) const { mapGetters, mapActions, Store } = Vuex new Vue({ el: '#app', store: new Store({ state: { color: 'red' }, getters: { color({color}) { return color } }, mutations: { setColor(state, payload) { state.color = payload } }, actions: { setColor({commit}, payload) { commit('setColor', payload) } } }), methods: { ...mapGetters([ 'color' ]), ...mapActions([ 'setColor' ]) }, computed: { computedColor: { set(value) { this.setColor(value) }, get() { return this.color() } }, style() { return `background-color: ${this.computedColor};` } }, watch: { computedColor() { console.log(`Watcher in use @${new Date().getTime()}`) } } }) 

See JSFiddle demo.

When you want to watch on state level, it can be done this way:

let App = new Vue({ //... store, watch: { '$store.state.myState': function (newVal) { console.log(newVal); store.dispatch('handleMyStateChange'); } }, //... }); 

Vue watch in string state

state:

$store.state.local_store.list_of_data 

inside component

 watch: { '$store.state.local_store.list_of_data':{//<----------your state call in string handler(){ console.log("value changeing in party sales entry"); //<---do your stuff here }, deep:true } }, 

A very simple method in which I use computed is something like this. May be it is of any help to you.

 const variable_name = computed( () => store.state.[name_of_state].property_name ); 

Another version in which you can do this is

computed: { name () { return this.$store.state.[name_of_state].property } } 

This is a format of accessing the getter from the store. Hope you have a great day.

You can also use mapState in your vue component to direct getting state from store.

In your component:

computed: mapState([ 'my_state' ]) 

Where my_state is a variable from the store.

I used this way and it works:

store.js:

const state = { createSuccess: false }; 

mutations.js

[mutations.CREATE_SUCCESS](state, payload) { state.createSuccess = payload; } 

actions.js

async [mutations.STORE]({ commit }, payload) { try { let result = await axios.post('/api/admin/users', payload); commit(mutations.CREATE_SUCCESS, user); } catch (err) { console.log(err); } } 

getters.js

isSuccess: state => { return state.createSuccess } 

And in your component where you use state from store:

watch: { isSuccess(value) { if (value) { this.$notify({ title: "Success", message: "Create user success", type: "success" }); } } } 

When user submit form, action STORE will be call, after created success, CREATE_SUCCESS mutation is committed after that. Turn createSuccess is true, and in component, watcher will see value has changed and trigger notification.

isSuccess should be match with the name you declare in getters.js

You can also watch it safely with debouncedWatch (vue use function)

 debouncedWatch( lines, () => { console.log('changed'); }, 500, );