web-utilities-vueuse

VueUse Composable Patterns

Quick Guide: VueUse provides 250+ composable functions for Vue 3 that wrap browser APIs, sensors, network, state, and component logic into reactive composables. Import individual functions from @vueuse/core for tree-shaking. All composables return reactive refs and follow Vue Composition API conventions. Use useLocalStorage for persistent state, useFetch for reactive HTTP, useIntersectionObserver for visibility detection, createGlobalState for shared state, and useVModel for two-way binding helpers. Always call composables in <script setup> or setup() synchronously. Clean up is automatic via Vue's lifecycle.

---

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST call VueUse composables synchronously inside <script setup> or setup() -- NEVER inside async callbacks, setTimeout, or conditional blocks)

(You MUST use shallowRef instead of ref for large objects/arrays in VueUse composables to avoid deep reactivity overhead)

(You MUST handle SSR by checking typeof window !== "undefined" or using VueUse's built-in SSR-safe composables -- browser APIs crash during server rendering)

(You MUST import individual composables from @vueuse/core -- NEVER use import * as vueuse which defeats tree-shaking)

</critical_requirements>

---

Auto-detection: VueUse, vueuse, @vueuse/core, @vueuse/integrations, useLocalStorage, useSessionStorage, useClipboard, useFetch, useMouse, useScroll, useIntersectionObserver, useResizeObserver, useElementVisibility, useMediaQuery, usePreferredDark, useDark, useToggle, useCounter, useCycleList, useWebSocket, useEventSource, useEventListener, useTransition, useRafFn, createGlobalState, useRefHistory, syncRef, useVModel, useVirtualList, onClickOutside, onKeyStroke, createFetch

When to use:

• Browser API access with reactive wrappers (localStorage, clipboard, media queries)
• Sensor data as reactive refs (mouse position, scroll, resize, intersection)
• Reactive HTTP requests with abort, refetch, and interceptors
• Global state shared across components without a state management library
• Component utilities (v-model helpers, virtual lists, keyboard shortcuts)
• SSR-safe browser API access

When NOT to use:

• Complex state management with actions/mutations (use a dedicated state solution)
• Server-side data fetching with caching/invalidation (use your data-fetching solution)
• Simple one-off operations that don't need reactivity
• Non-Vue projects (VueUse depends on Vue 3's reactivity system)

Key patterns covered:

• Core utilities (useToggle, useCounter, useCycleList)
• Browser composables (useLocalStorage, useClipboard, useMediaQuery, useEventListener)
• Sensor composables (useMouse, useScroll, useIntersectionObserver, useResizeObserver)
• Network composables (useFetch, useWebSocket, useEventSource)
• State composables (createGlobalState, useRefHistory, syncRef)
• Component composables (useVModel, useVirtualList, onClickOutside, onKeyStroke)
• Animation composables (useTransition, useRafFn)

Detailed Resources:

• examples/core.md - Core utilities, browser APIs, event listeners
• examples/sensors.md - Mouse, scroll, intersection, resize, visibility
• examples/network.md - useFetch, useWebSocket, useEventSource
• examples/state.md - createGlobalState, useRefHistory, syncRef, persistence
• examples/component.md - useVModel, useVirtualList, onClickOutside, onKeyStroke
• reference.md - Composable decision framework, SSR guide, gotchas

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Philosophy

VueUse follows the Composition API composable pattern: encapsulate reactive logic in reusable functions that return refs and methods. Each composable wraps a single concern (a browser API, sensor, or utility) and handles setup/teardown automatically via Vue's lifecycle.

Key principle: VueUse composables are designed for tree-shaking. Import only what you use -- each function is independently importable with minimal overhead.

import { useLocalStorage, useDark, useMediaQuery } from "@vueuse/core";

// Reactive localStorage -- syncs across tabs
const userName = useLocalStorage("user-name", "Guest");

// Dark mode with auto-detection
const isDark = useDark();

// Responsive breakpoint
const MOBILE_BREAKPOINT = "(max-width: 768px)";
const isMobile = useMediaQuery(MOBILE_BREAKPOINT);

When to Use VueUse

• Wrapping browser APIs with reactivity (localStorage, clipboard, geolocation)
• Tracking DOM state reactively (scroll position, element visibility, mouse)
• Lightweight global state without full store setup
• Component utilities (keyboard shortcuts, click outside, virtual lists)
• Reactive data fetching for simple cases

When NOT to Use VueUse

• Complex server state with caching, invalidation, optimistic updates (use your data-fetching solution)
• Complex client state with computed derivations and devtools (use a dedicated state solution)
• Non-Vue projects (the reactivity system is Vue-specific)
• When native browser API is sufficient without reactivity

Current Version

VueUse v14.x is the current stable release, supporting Vue 3.5+. All composables are written in TypeScript with full type inference.

---

Core Patterns

Pattern 1: Reactive Storage (useLocalStorage, useSessionStorage)

Persistent reactive state that syncs with browser storage and across tabs.

<script setup lang="ts">
import { useLocalStorage, useSessionStorage } from "@vueuse/core";

interface UserPreferences {
  theme: "light" | "dark";
  fontSize: number;
  sidebarCollapsed: boolean;
}

const DEFAULT_PREFERENCES: UserPreferences = {
  theme: "light",
  fontSize: 14,
  sidebarCollapsed: false,
};

// ✅ Good Example - Typed reactive localStorage
const preferences = useLocalStorage<UserPreferences>(
  "user-prefs",
  DEFAULT_PREFERENCES,
);

// Read and write like a normal ref
preferences.value.theme = "dark"; // auto-persists to localStorage

// Session-only storage (cleared on tab close)
const sessionToken = useSessionStorage("session-token", "");

// Remove from storage
preferences.value = null; // removes the key from localStorage
</script>

Why good: automatic serialization/deserialization, cross-tab sync via storage events, typed with generics, cleanup is automatic

// ❌ Bad Example - Manual localStorage
const prefs = ref(JSON.parse(localStorage.getItem("user-prefs") ?? "null"));

watch(
  prefs,
  (val) => {
    localStorage.setItem("user-prefs", JSON.stringify(val)); // manual sync
  },
  { deep: true },
);
// No cross-tab sync, no automatic cleanup, error-prone serialization

Why bad: manual serialization is error-prone, no cross-tab sync, no SSR safety, deep watcher on every change is expensive

---

Pattern 2: Event Listeners (useEventListener)

Auto-cleaned event listeners with type safety.

<script setup lang="ts">
import { useEventListener } from "@vueuse/core";
import { useTemplateRef } from "vue";

const buttonRef = useTemplateRef("button");

// ✅ Good Example - Auto-cleanup event listeners
// Automatically removed when component unmounts
useEventListener(window, "resize", () => {
  console.log("Window resized:", window.innerWidth);
});

// Works with template refs -- waits for mount
useEventListener(buttonRef, "click", (event) => {
  console.log("Button clicked:", event);
});

// Multiple events on same target
useEventListener(document, "visibilitychange", () => {
  console.log("Visibility:", document.visibilityState);
});
</script>

Why good: automatic cleanup on unmount prevents memory leaks, handles ref lifecycle (waits for mount), type-safe event names

// ❌ Bad Example - Manual event listener
onMounted(() => {
  window.addEventListener("resize", handleResize);
});
onUnmounted(() => {
  window.removeEventListener("resize", handleResize); // easy to forget!
});

Why bad: manual add/remove is error-prone -- missing onUnmounted cleanup causes memory leaks

---

Pattern 3: Media Queries and Dark Mode

Reactive responsive design and theme management.

<script setup lang="ts">
import {
  useMediaQuery,
  usePreferredDark,
  useDark,
  useToggle,
} from "@vueuse/core";

// ✅ Good Example - Reactive breakpoints
const MOBILE_BREAKPOINT = "(max-width: 768px)";
const TABLET_BREAKPOINT = "(min-width: 769px) and (max-width: 1024px)";

const isMobile = useMediaQuery(MOBILE_BREAKPOINT);
const isTablet = useMediaQuery(TABLET_BREAKPOINT);

// System preference detection
const prefersDark = usePreferredDark();

// Full dark mode with toggle (adds class to html element)
const isDark = useDark();
const toggleDark = useToggle(isDark);
</script>

<template>
  <nav :class="{ 'nav--compact': isMobile }">
    <button @click="toggleDark()">
      {{ isDark ? "Light Mode" : "Dark Mode" }}
    </button>
  </nav>
</template>

Why good: reactive media queries update the ref automatically on resize, useDark handles class toggling and persistence, useToggle provides a clean toggle function

---

Pattern 4: Clipboard Access

Reactive clipboard API with permission handling.

<script setup lang="ts">
import { useClipboard } from "@vueuse/core";

// ✅ Good Example - Clipboard with feedback
const source = ref("Text to copy");
const { text, copy, copied, isSupported } = useClipboard({ source });

async function handleCopy(): Promise<void> {
  await copy(); // copies source.value to clipboard
  // `copied` ref is true for 1.5s (default) after copy
}
</script>

<template>
  <div v-if="isSupported">
    <button @click="handleCopy">
      {{ copied ? "Copied!" : "Copy" }}
    </button>
  </div>
  <div v-else>Clipboard API not supported</div>
</template>

Why good: isSupported check for graceful degradation, copied provides automatic feedback timing, source reactive binding

---

Pattern 5: Core Utilities (useToggle, useCounter, useCycleList)

Simple reactive utilities for common state patterns.

<script setup lang="ts">
import { useToggle, useCounter, useCycleList } from "@vueuse/core";

// ✅ Good Example - Toggle state
const [isOpen, toggleOpen] = useToggle(false);

// Counter with bounds
const MIN_COUNT = 0;
const MAX_COUNT = 100;
const { count, inc, dec, reset } = useCounter(0, {
  min: MIN_COUNT,
  max: MAX_COUNT,
});

// Cycle through options
const themes = ["light", "dark", "auto"] as const;
const {
  state: currentTheme,
  next: nextTheme,
  prev: prevTheme,
} = useCycleList([...themes]);
</script>

<template>
  <div>
    <button @click="toggleOpen()">{{ isOpen ? "Close" : "Open" }}</button>
    <div>
      <button @click="dec()">-</button>
      <span>{{ count }}</span>
      <button @click="inc()">+</button>
    </div>
    <button @click="nextTheme()">Theme: {{ currentTheme }}</button>
  </div>
</template>

Why good: eliminates boilerplate for common patterns, useCounter enforces min/max bounds, useCycleList handles wrapping automatically

---

Pattern 6: useFetch for Reactive HTTP

Reactive data fetching with abort, refetch, and interceptors.

<script setup lang="ts">
import { useFetch } from "@vueuse/core";
import { computed } from "vue";

const userId = ref(1);
const apiUrl = computed(() => `/api/users/${userId.value}`);

// ✅ Good Example - Reactive fetch with auto-refetch
const { data, isFetching, error, abort } = useFetch(apiUrl, {
  refetch: true, // re-fetches when apiUrl changes
}).json<User>();

// Manual fetch with immediate: false
const { data: submitResult, execute } = useFetch("/api/submit", {
  immediate: false,
})
  .post(formData)
  .json();

async function handleSubmit(): Promise<void> {
  await execute(); // manually trigger the fetch
}
</script>

Why good: URL reactivity triggers automatic refetch, .json<T>() provides type-safe parsing, abort for cancellation, immediate: false for manual control

See examples/network.md for createFetch, interceptors, and advanced patterns.

---

Pattern 7: createGlobalState for Shared State

Lightweight global state without a state management library.

// stores/counter.ts
import { createGlobalState } from "@vueuse/core";
import { computed, shallowRef } from "vue";

// ✅ Good Example - Global state with computed
export const useGlobalCounter = createGlobalState(() => {
  const count = shallowRef(0);
  const doubleCount = computed(() => count.value * 2);
  const isPositive = computed(() => count.value > 0);

  function increment(): void {
    count.value++;
  }

  function decrement(): void {
    count.value--;
  }

  function reset(): void {
    count.value = 0;
  }

  return { count, doubleCount, isPositive, increment, decrement, reset };
});

<!-- Any component can use the shared state -->
<script setup lang="ts">
import { useGlobalCounter } from "@/stores/counter";

const { count, doubleCount, increment, decrement } = useGlobalCounter();
</script>

Why good: shared state across components, no provider/inject boilerplate, composable pattern with computed derivations, shallowRef for performance

---

<red_flags>

RED FLAGS

High Priority:

• Calling composables inside async functions, setTimeout, or event handlers -- composables must be called synchronously in setup() to bind to the component lifecycle
• Using ref instead of shallowRef for large objects in storage composables -- causes unnecessary deep reactivity tracking on every nested property
• Accessing browser APIs without SSR guards -- useLocalStorage, useClipboard, useMouse crash during server-side rendering

Medium Priority:

• Using import * from "@vueuse/core" -- defeats tree-shaking, imports the entire 250+ function library
• Not using isSupported check from composables that wrap browser APIs -- causes runtime errors in unsupported environments
• Creating custom composables for functionality VueUse already provides -- check the docs first
• Using watch + ref to track DOM state that VueUse composables handle reactively (useMouse, useScroll, etc.)

Gotchas & Edge Cases:

• useLocalStorage returns a RemovableRef -- setting .value = null removes the key from storage entirely, not storing null
• useFetch with refetch: true fires immediately AND on URL change -- use immediate: false if you only want manual control
• createGlobalState creates a singleton per import -- state persists until page reload, even after all components unmount
• useIntersectionObserver callback fires immediately with current state on creation -- don't assume first callback means element just became visible
• useDark modifies the html element's class -- ensure your CSS expects the class name it adds (default: dark)
• useWebSocket auto-reconnects by default -- pass autoReconnect: false if you want manual control
• useEventListener with a template ref waits for onMounted internally -- the listener is NOT active during setup()
• useRefHistory tracks every change by default -- use { deep: false } for shallow tracking or useManualRefHistory for explicit snapshots

</red_flags>

---

<critical_reminders>

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md

(You MUST call VueUse composables synchronously inside <script setup> or setup() -- NEVER inside async callbacks, setTimeout, or conditional blocks)

(You MUST use shallowRef instead of ref for large objects/arrays in VueUse composables to avoid deep reactivity overhead)

(You MUST handle SSR by checking typeof window !== "undefined" or using VueUse's built-in SSR-safe composables -- browser APIs crash during server rendering)

(You MUST import individual composables from @vueuse/core -- NEVER use import * as vueuse which defeats tree-shaking)

Failure to follow these rules will cause SSR crashes, performance degradation, and lifecycle errors.

</critical_reminders>