A composable is a reusable function that encapsulates stateful logic using the Composition API. By convention it's named useXxx and returns reactive state plus functions — letting you share logic across components without mixins or repetition.
{ ref, computed } ;
() {
count = (initial);
double = ( count. * );
() { count.++; }
() { count. = initial; }
{ count, double, increment, reset };
}
<script setup>
import { useCounter } from "@/composables/useCounter";
const { count, double, increment } = useCounter(10); // each call = independent state
</script>
<template>
<button @click="increment">{{ count }} (double: {{ double }})</button>
</template>
Each component that calls useCounter() gets its own isolated count — composables create fresh state per call, unlike a shared module-level variable.
import { ref, onUnmounted } from "vue";
export function useMousePosition() {
const x = ref(0), y = ref(0);
const update = (e) => { x.value = e.pageX; y.value = e.pageY; };
window.addEventListener("mousemove", update); // set up
onUnmounted(() => window.removeEventListener("mousemove", update)); // auto cleanup!
return { x, y };
}
Composables can use lifecycle hooks, watchers, and other composables — and crucially, they encapsulate their own cleanup (onUnmounted), so consumers don't have to remember it.
Mixins (Vue 2): merged into the component — unclear where properties came from,
naming collisions between mixins, implicit dependencies
Composables: explicit imports + return values — clear sources, no collisions,
can be composed, fully typed in TypeScript
Composables are the idiomatic way to extract and reuse stateful logic in Vue 3 — data fetching, form handling, mouse/scroll tracking, debouncing, etc.
They solve the logic-reuse problem cleanly (explicit, collision-free, composable, TypeScript-friendly) where Vue 2's mixins failed.
They're the primary reason teams adopt the Composition API: shared logic becomes a simple, testable function rather than scattered or duplicated code.