charging-cabinet/software/h5-uniapp/.agents/skills/vue-best-practices/reference/v-if-vs-v-show-performance.md

title, impact, impactDescription, type, tags

title	impact	impactDescription	type	tags
Choose v-if or v-show Based on Toggle Frequency	MEDIUM	Wrong choice causes unnecessary DOM operations or wasted initial render cost	capability	vue3 conditional-rendering v-if v-show performance

Choose v-if or v-show Based on Toggle Frequency

Impact: MEDIUM - Using the wrong directive for your use case leads to suboptimal performance. v-if has higher toggle costs (destroys/recreates elements), while v-show has higher initial render costs (always in DOM). Choosing incorrectly can cause unnecessary DOM manipulation or waste memory on hidden elements.

v-if is "real" conditional rendering that properly destroys and recreates event listeners and child components. v-show just toggles CSS display property, keeping everything in the DOM.

Task Checklist

• Use v-show for elements that toggle frequently (modals, dropdowns, panels)
• Use v-if for conditions that rarely change at runtime (auth states, feature flags)
• Use v-if when initial condition is likely false (lazy rendering saves cost)
• Use v-if when child components have expensive setup/teardown
• Consider the memory cost of keeping hidden elements in DOM with v-show

Incorrect:

<!-- WRONG: Frequent toggle with v-if causes expensive DOM operations -->
<template>
  <button @click="showPanel = !showPanel">Toggle</button>

  <!-- User clicks this frequently - v-if destroys/recreates every time -->
  <div v-if="showPanel" class="settings-panel">
    <ComplexForm />
  </div>
</template>

<!-- WRONG: Rarely-true condition with v-show wastes initial render -->
<template>
  <!-- Admin panel shown only for admin users (rare), but v-show renders it for everyone -->
  <AdminPanel v-show="user.isAdmin" />
</template>

Correct:

<!-- CORRECT: Frequent toggle with v-show - cheap CSS toggle -->
<template>
  <button @click="showPanel = !showPanel">Toggle</button>

  <!-- v-show just toggles display: none, no DOM destruction -->
  <div v-show="showPanel" class="settings-panel">
    <ComplexForm />
  </div>
</template>

<!-- CORRECT: Rare condition with v-if - lazy rendering -->
<template>
  <!-- Only rendered for admins, non-admins don't pay the render cost -->
  <AdminPanel v-if="user.isAdmin" />
</template>

<!-- CORRECT: Auth-gated content with v-if -->
<template>
  <!-- v-if is ideal here - auth state rarely changes -->
  <div v-if="isAuthenticated">
    <UserDashboard />
  </div>
  <div v-else>
    <LoginPrompt />
  </div>
</template>

Decision Guide

Scenario	Recommendation	Reason
Toggle frequently (tabs, accordions, dropdowns)	v-show	Cheap CSS toggle
Toggle rarely (auth, feature flags)	v-if	Lazy render, clean DOM
Initially false, may never be true	v-if	Never pays render cost
Complex child components with state	v-if	Properly resets state on toggle
Need to preserve component state across toggles	v-show	Component stays alive

Key Differences

// v-if behavior:
// - Condition false: Element NOT in DOM, child components NOT created
// - Condition true: Element added, child components created, mounted hooks fire
// - Condition false again: Element removed, child components destroyed, unmounted hooks fire

// v-show behavior:
// - Condition false: Element IN DOM with display: none, child components exist
// - Condition true: display: none removed
// - Component lifecycle hooks only fire once (on initial mount)

Reference

• Vue.js Conditional Rendering - v-if vs v-show