v-for renders a list of elements by iterating over an array (or object/range). You should always pair it with a unique :key so Vue can track items efficiently.
<script setup>
import { ref } from "vue";
const items = ref([{ id: 1, name: "Apple" }, { id: 2, name: "Banana" }]);
</script>
<template>
<ul>
<li v-for="item in items" :key="item.id">{{ item.name }}</li>
</ul>
</template>
<template>
<li v-for="(item, index) in items" :key="item.id">{{ index }}: {{ item.name }}</li>
<li v-for="(value, key) in myObject" :key="key">{{ key }}: {{ value }}</li>
<span v-for="n in 5" :key="n">{{ n }}</span> <!-- range 1..5 -->
</template>
Vue uses the key to identify which items changed, were added, or removed, so it can reuse and reorder existing DOM nodes instead of rebuilding them. Without a stable key, Vue falls back to an "in-place patch" strategy that can cause bugs:
<!-- ❌ using index as key → wrong when the list reorders/filters -->
<li v-for="(item, i) in items" :key="i">
<input /> <!-- input state can attach to the WRONG item after reordering -->
</li>
<!-- ✅ stable unique id → Vue tracks each item correctly -->
<li v-for="item in items" :key="item.id">...</li>
Using the array index as the key is a common mistake — when items are reordered, inserted, or deleted, component/DOM state (like input values or checkbox states) can stick to the wrong row.
<!-- ❌ avoid — ambiguous precedence -->
<li v-for="x in items" v-if="x.active">...</li>
<!-- ✅ filter in a computed, or wrap with <template v-for> -->
v-for is how you render dynamic lists.
The :key is not optional in practice: a stable, unique key lets Vue's virtual DOM diff efficiently and avoids subtle state-mismatch bugs on reorder/filter.
Knowing to use a real id (never the index for dynamic lists) and to keep v-for/v-if separate is essential for correct, performant lists.