Suggest an editImprove this articleRefine the answer for “What is state in the context of Vue.js?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**State** in the context of Vue.js is **data** that is stored inside a component or application and **can change over time**, causing the **interface to re-render**. **Key point:** state is what determines what the user sees on the screen; when state changes, the UI changes.Shown above the full answer for quick recall.Answer (EN)Image**State** in the context of Vue.js is **data** that is stored inside a component or application and **can change over time**, causing the **interface to re-render**. In other words: - **State is what determines what the user sees on the screen.** - When state changes, the UI changes. --- ## Where is state stored? In Vue 3, state is most often created using **reactive()** or **ref()**: ```javascript <script setup> import { ref } from 'vue' // this is state const count = ref(0) </script> ``` `count` is state. When `count.value` changes, Vue automatically updates the interface. --- ## Example: state in a component ```javascript <template> <button @click="count++"> Count: {{ count }} </button> </template> <script setup> import { ref } from 'vue' const count = ref(0) // <- the component's state </script> ``` The UI updates every time we change `count`. --- ## Why does state matter? Because the UI depends on data. For example: - whether a modal is open - text entered into a form - which tab is selected - the list of products in a cart - data fetched from an API - the current user All of this is **state**. --- ## How does Vue react to state changes? Vue uses **reactivity**: it tracks which data is used in the template or in computed values. When you change state: ```javascript count.value++ ``` Vue: 1. records the change 2. figures out which parts of the UI are affected 3. re-renders only the components that need it This is what makes the application fast. --- ## Types of state in Vue ### 1) **Local state** Stored in the component. Example: the state of a modal, an input, a counter. ```javascript const isOpen = ref(false) ``` ### 2) **Global state** Used throughout the whole application. Stored in: - **Pinia** - in older projects, Vuex Example: authentication state, a cart, user settings. ```javascript export const useUserStore = defineStore('user', { state: () => ({ user: null }) }) ``` --- ## State from props Sometimes state is passed top-down by the parent: ```javascript <ChildComponent :title="pageTitle" /> ``` Here `pageTitle` is also the parent's state. --- ## State + UI: a simple example ```javascript <template> <input v-model="name" placeholder="Enter your name" /> <p>Hello, {{ name }}!</p> </template> <script setup> import { ref } from 'vue' const name = ref('') // state </script> ``` We change `name` -> Vue updates the displayed text. --- ## What is NOT state? - Constants - imported data - computed properties (they depend on state, but don't store state themselves) - props inside the parent (they become state in the child only if handled locally) --- ## Summary (short) **State in Vue is mutable data that the UI depends on.** **When state changes, Vue automatically updates the interface.** State can be: - local (inside a component), - global (Pinia/Vuex), - passed via props.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.