Tutorial

Persist Vuex State with vuex-persist

Published on August 7, 2017
author

Joshua Bemenderfer

Persist Vuex State with vuex-persist

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Vuex is great for handling state in your app, but sometimes you want it to persist across multiple pages loads and whatnot. The naive way to do this (and I’m as guilty of it as any,) is to add a quick little function call in each mutation to save the current state of your app to localStorage. Not exactly a great solution, but just not-bad-enough that it often suffices. But there’s a better way. Vuex actually has plugin support, and vuex-persist is a teeny-tiny plugin that automatically syncs your store with localStorage, or any other storage method supporting the getItem/setItem/clear interface.

Installation

Install vuex-persist in your Vue.js project.

# Yarn
$ yarn add vuex-persist
# or NPM
$ npm install vuex-persist --save

Usage

Now, wherever you initialize your store (and this may vary a lot from project to project,) import vuex-persist and initialize it as a plugin for Vuex.

main.js (Partial)
import Vue from 'vue'
import App from 'App.vue';
import Vuex 'vuex';
import VuexPersist from 'vuex-persist';


Vue.use(Vuex);

const vuexLocalStorage = new VuexPersist({
  key: 'vuex' // The key to store the state on in the storage provider.
  storage: window.localStorage, // or window.sessionStorage or localForage
  // Function that passes the state and returns the state with only the objects you want to store.
  // reducer: state => state,
  // Function that passes a mutation and lets you decide if it should update the state in localStorage.
  // filter: mutation => (true)
})

const store = new Vuex.Store({
  ...
  plugins: [vuexLocalStorage.plugin]
});

...

new Vue({
  store,
  el: '#app',
  render: h => h(App)
});

Using the reducer option.

The reducer option allows you to only store certain sections of the state. It’s a simple function that gets passed the full state tree and is expected to return an object containing only the parts of the state tree you’d like to keep. This shouldn’t, however, modify the structure of the tree, or otherwise it can’t be re-loaded.

const vuexLocalStorage = new VuexPersist({
  storage: window.localStorage, // or window.sessionStorage or localForage instance.
  // Function that passes the state and returns the state with only the objects you want to store.
  reducer: state => ({
    keepThisModule: state.keepThisModule,
    keepThisModuleToo: state.keepThisModuleToo
    // getRidOfThisModule: state.getRidOfThisModule (No one likes it.)
  })
})

Using the filter option.

Sometimes certain mutations shouldn’t trigger a store sync. For example, if you have a mutation called every few milliseconds, updating the storage every time it’s called would cause a huge degredation in performance. vuex-persist provides a filter function to address this exact use-case. You can filter out any mutations you don’t want to cause a storage update, or create a whitelist of mutations you want to keep.

const badMutations = [
  'someMutationThatGetsCalledTooOften'
]

const vuexLocalStorage = new VuexPersist({
  storage: window.localStorage, // or window.sessionStorage or localForage
  // Function that passes the state and returns the state with only the objects you want to store.
  // someMutationThatGetsCalledTooOften gets ignored
  filter: mutation => (badMutations.indexOf(mutation.type) === -1) // Boolean
})

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About the authors
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Joshua Bemenderfer

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“keepThisModule” is a misleading name. One might think this store is module based. “reducer” option is for root state properties only. Use “modules” config option to whitelist actual modules.

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