Never Use v-if and v-for on the Same Element
Impact: HIGH - Using v-if and v-for on the same element creates ambiguous precedence that differs between Vue 2 and Vue 3. In Vue 2, v-for had higher precedence; in Vue 3, v-if has higher precedence. This breaking change causes subtle bugs during migration and makes code intent unclear.
The ESLint rule vue/no-use-v-if-with-v-for enforces this best practice.
Task Checklist
- Never place v-if and v-for on the same element
- For filtering list items: use a computed property that filters the array
- For hiding entire list: wrap with
<template v-if>around the v-for - Enable eslint-plugin-vue rule
vue/no-use-v-if-with-v-for
Incorrect:
<!-- WRONG: v-if and v-for on same element - ambiguous precedence -->
<template>
<!-- Intent: show only active users -->
<li v-for="user in users" v-if="user.isActive" :key="user.id">
{{ user.name }}
</li>
</template><!-- WRONG: Hiding entire list conditionally -->
<template>
<li v-for="user in users" v-if="shouldShowList" :key="user.id">
{{ user.name }}
</li>
</template><!-- WRONG: Vue 3 precedence issue -->
<template>
<!-- In Vue 3, v-if runs FIRST, so 'user' is undefined! -->
<li v-for="user in users" v-if="user.isActive" :key="user.id">
{{ user.name }}
</li>
<!-- Error: Cannot read property 'isActive' of undefined -->
</template>Correct:
<!-- CORRECT: Filter with computed property -->
<template>
<li v-for="user in activeUsers" :key="user.id">
{{ user.name }}
</li>
</template>
<script setup>
import { computed } from 'vue'
const props = defineProps(['users'])
const activeUsers = computed(() =>
props.users.filter(user => user.isActive)
)
</script><!-- CORRECT: Wrap with <template v-if> for conditional list -->
<template>
<template v-if="shouldShowList">
<li v-for="user in users" :key="user.id">
{{ user.name }}
</li>
</template>
</template><!-- CORRECT: v-if inside the loop (per-item condition) -->
<template>
<ul>
<template v-for="user in users" :key="user.id">
<li v-if="user.isActive">
{{ user.name }}
</li>
</template>
</ul>
</template>Vue 2 vs Vue 3 Precedence Change
// Vue 2: v-for evaluated first
// <li v-for="user in users" v-if="user.isActive">
// Equivalent to: users.forEach(user => { if (user.isActive) render(user) })
// Vue 3: v-if evaluated first
// <li v-for="user in users" v-if="user.isActive">
// Equivalent to: if (user.isActive) users.forEach(user => render(user))
// Problem: 'user' doesn't exist yet when v-if runs!Why Computed Properties Are Better
// Benefits of filtering via computed:
// 1. Clear separation of concerns (logic vs template)
// 2. Cached - only recalculates when dependencies change
// 3. Reusable - can be used elsewhere in component
// 4. Testable - can unit test the filtering logic
// 5. No ambiguity about intent
const activeUsers = computed(() =>
users.value.filter(u => u.isActive)
)
// Can add more complex filtering
const filteredUsers = computed(() =>
users.value
.filter(u => u.isActive)
.filter(u => u.role === selectedRole.value)
.sort((a, b) => a.name.localeCompare(b.name))
)