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<!DOCTYPE HTML> <html lang="en" > <head> <meta charset="UTF-8"> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> <title>Getters · Vuex</title> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="description" content=""> <meta name="generator" content="GitBook 3.2.3"> <link rel="stylesheet" href="../gitbook/style.css"> <link rel="stylesheet" href="../gitbook/gitbook-plugin-prism/prism.css"> <link rel="stylesheet" href="../gitbook/gitbook-plugin-search/search.css"> <link rel="stylesheet" href="../gitbook/gitbook-plugin-theme-vuejs/vue.css"> <meta name="HandheldFriendly" content="true"/> <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no"> <meta name="apple-mobile-web-app-capable" content="yes"> <meta name="apple-mobile-web-app-status-bar-style" content="black"> <link rel="apple-touch-icon-precomposed" sizes="152x152" href="../gitbook/images/apple-touch-icon-precomposed-152.png"> <link rel="shortcut icon" href="../gitbook/images/favicon.ico" type="image/x-icon"> <link rel="next" href="mutations.html" /> <link rel="prev" href="state.html" /> </head> <body> <div class="book"> <div class="book-summary"> <div id="book-search-input" role="search"> <input type="text" placeholder="Type to search" /> </div> <nav role="navigation"> <script async type="text/javascript" src="//cdn.carbonads.com/carbon.js?zoneid=1673&serve=C6AILKT&placement=vuejs" id="_carbonads_js"></script> <ul class="summary"> <li class="chapter " data-level="1.1" data-path="./"> <a href="./"> Introduction </a> </li> <li class="chapter " data-level="1.2" > <a target="_blank" href="https://github.com/vuejs/vuex/releases"> Release Notes </a> </li> <li class="chapter " data-level="1.3" data-path="installation.html"> <a href="installation.html"> Installation </a> </li> <li class="chapter " data-level="1.4" data-path="intro.html"> <a href="intro.html"> What is Vuex? </a> </li> <li class="chapter " data-level="1.5" data-path="getting-started.html"> <a href="getting-started.html"> Getting Started </a> </li> <li class="chapter " data-level="1.6" data-path="core-concepts.html"> <a href="core-concepts.html"> Core Concepts </a> <ul class="articles"> <li class="chapter " data-level="1.6.1" data-path="state.html"> <a href="state.html"> State </a> </li> <li class="chapter active" data-level="1.6.2" data-path="getters.html"> <a href="getters.html"> Getters </a> </li> <li class="chapter " data-level="1.6.3" data-path="mutations.html"> <a href="mutations.html"> Mutations </a> </li> <li class="chapter " data-level="1.6.4" data-path="actions.html"> <a href="actions.html"> Actions </a> </li> <li class="chapter " data-level="1.6.5" data-path="modules.html"> <a href="modules.html"> Modules </a> </li> </ul> </li> <li class="chapter " data-level="1.7" data-path="structure.html"> <a href="structure.html"> Application Structure </a> </li> <li class="chapter " data-level="1.8" data-path="plugins.html"> <a href="plugins.html"> Plugins </a> </li> <li class="chapter " data-level="1.9" data-path="strict.html"> <a href="strict.html"> Strict Mode </a> </li> <li class="chapter " data-level="1.10" data-path="forms.html"> <a href="forms.html"> Form Handling </a> </li> <li class="chapter " data-level="1.11" data-path="testing.html"> <a href="testing.html"> Testing </a> </li> <li class="chapter " data-level="1.12" data-path="hot-reload.html"> <a href="hot-reload.html"> Hot Reloading </a> </li> <li class="chapter " data-level="1.13" data-path="api.html"> <a href="api.html"> API Reference </a> </li> <li class="divider"></li> <li> <a href="https://www.gitbook.com" target="blank" class="gitbook-link"> Published with GitBook </a> </li> </ul> </nav> </div> <div class="book-body"> <div class="body-inner"> <div class="book-header" role="navigation">  <h1> <a href="." >Getters</a> </h1> </div> <div class="page-wrapper" tabindex="-1" role="main"> <div class="page-inner"> <div id="book-search-results"> <div class="search-noresults"> <section class="normal markdown-section"> <h1 id="getters">Getters</h1> Sometimes we may need to compute derived state based on store state, for example filtering through a list of items and counting them: <pre class="language-"><code class="lang-js">computed: { doneTodosCount () { return this.$store.state.todos.filter(todo => todo.done).length } } </code></pre> If more than one component needs to make use of this, we have to either duplicate the function, or extract it into a shared helper and import it in multiple places - both are less than ideal. Vuex allows us to define "getters" in the store. You can think of them as computed properties for stores. Like computed properties, a getter's result is cached based on its dependencies, and will only re-evaluate when some of its dependencies have changed. Getters will receive the state as their 1st argument: <pre class="language-"><code class="lang-js">const store = new Vuex.Store({ state: { todos: [ { id: 1, text: '...', done: true }, { id: 2, text: '...', done: false } ] }, getters: { doneTodos: state => { return state.todos.filter(todo => todo.done) } } }) </code></pre> The getters will be exposed on the <code>store.getters</code> object: <pre class="language-"><code class="lang-js">store.getters.doneTodos // -> [{ id: 1, text: '...', done: true }] </code></pre> Getters will also receive other getters as the 2nd argument: <pre class="language-"><code class="lang-js">getters: { // ... doneTodosCount: (state, getters) => { return getters.doneTodos.length } } </code></pre> <pre class="language-"><code class="lang-js">store.getters.doneTodosCount // -> 1 </code></pre> We can now easily make use of it inside any component: <pre class="language-"><code class="lang-js">computed: { doneTodosCount () { return this.$store.getters.doneTodosCount } } </code></pre> You can also pass arguments to getters by returning a function. This is particularly useful when you want to query an array in the store: <pre class="language-"><code class="lang-js">getters: { // ... getTodoById: (state) => (id) => { return state.todos.find(todo => todo.id === id) } } </code></pre> <pre class="language-"><code class="lang-js">store.getters.getTodoById(2) // -> { id: 2, text: '...', done: false } </code></pre> <h3 id="the-mapgetters-helper">The <code>mapGetters</code> Helper</h3> The <code>mapGetters</code> helper simply maps store getters to local computed properties: <pre class="language-"><code class="lang-js">import { mapGetters } from 'vuex' export default { // ... computed: { // mix the getters into computed with object spread operator ...mapGetters([ 'doneTodosCount', 'anotherGetter', // ... ]) } } </code></pre> If you want to map a getter to a different name, use an object: <pre class="language-"><code class="lang-js">...mapGetters({ // map `this.doneCount` to `store.getters.doneTodosCount` doneCount: 'doneTodosCount' }) </code></pre> </section> </div> <div class="search-results"> <div class="has-results"> <h1 class="search-results-title"> results matching ""</h1> <ul class="search-results-list"></ul> </div> <div class="no-results"> <h1 class="search-results-title">No results matching ""</h1> </div> </div> </div> </div> </div> <script src="//m.servedby-buysellads.com/monetization.js" type="text/javascript"></script> <div class="bsa-cpc"></div> <script> (function(){ if(typeof _bsa !== 'undefined' && _bsa) { _bsa.init('default', 'CKYD62QM', 'placement:vuejsorg', { target: '.bsa-cpc', align: 'horizontal', disable_css: 'true' }); } })(); </script> </div> <a href="state.html" class="navigation navigation-prev " aria-label="Previous page: State"> </a> <a href="mutations.html" class="navigation navigation-next " aria-label="Next page: Mutations"> </a> </div> <script> var gitbook = gitbook || []; gitbook.push(function() { gitbook.page.hasChanged({"page":{"title":"Getters","level":"1.6.2","depth":2,"next":{"title":"Mutations","level":"1.6.3","depth":2,"path":"mutations.md","ref":"mutations.md","articles":[]},"previous":{"title":"State","level":"1.6.1","depth":2,"path":"state.md","ref":"state.md","articles":[]},"dir":"ltr"},"config":{"plugins":["edit-link","prism","-highlight","github","-highlight","github"],"styles":{"website":"styles/website.css","pdf":"styles/pdf.css","epub":"styles/epub.css","mobi":"styles/mobi.css","ebook":"styles/ebook.css","print":"styles/print.css"},"pluginsConfig":{"prism":{},"github":{"url":"https://github.com/vuejs/vuex/"},"livereload":{},"search":{},"theme-vuejs":{},"lunr":{"maxIndexSize":1000000,"ignoreSpecialCharacters":false},"sharing":{"facebook":false,"twitter":false,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"edit-link":{"label":"Edit This Page","base":"https://github.com/vuejs/vuex/tree/dev/docs"},"theme-default":{"styles":{"website":"styles/website.css","pdf":"styles/pdf.css","epub":"styles/epub.css","mobi":"styles/mobi.css","ebook":"styles/ebook.css","print":"styles/print.css"},"showLevel":false}},"theme":"default","pdf":{"pageNumbers":true,"fontSize":12,"fontFamily":"Arial","paperSize":"a4","chapterMark":"pagebreak","pageBreaksBefore":"/","margin":{"right":62,"left":62,"top":56,"bottom":56}},"structure":{"langs":"LANGS.md","readme":"README.md","glossary":"GLOSSARY.md","summary":"SUMMARY.md"},"variables":{},"title":"Vuex","language":"en","links":{"sharing":{"facebook":false,"twitter":false}},"gitbook":"2.x.x"},"file":{"path":"getters.md","mtime":"2018-02-17T07:20:49.000Z","type":"markdown"},"gitbook":{"version":"3.2.3","time":"2018-03-02T20:43:43.208Z"},"basePath":".","book":{"language":"en"}}); }); </script> </div> <script src="../gitbook/gitbook.js"></script> <script src="../gitbook/theme.js"></script> <script src="../gitbook/gitbook-plugin-edit-link/plugin.js"></script> <script src="../gitbook/gitbook-plugin-github/plugin.js"></script> <script src="../gitbook/gitbook-plugin-livereload/plugin.js"></script> <script src="../gitbook/gitbook-plugin-search/search-engine.js"></script> <script src="../gitbook/gitbook-plugin-search/search.js"></script> <script src="../gitbook/gitbook-plugin-lunr/lunr.min.js"></script> <script src="../gitbook/gitbook-plugin-lunr/search-lunr.js"></script> <script src="../gitbook/gitbook-plugin-sharing/buttons.js"></script> </body> </html>