charging-cabinet/software/h5-uniapp/.agents/skills/vue-best-practices/reference/keepalive-memory-management.md

title, impact, impactDescription, type, tags

title	impact	impactDescription	type	tags
KeepAlive Memory Management - Prevent Memory Leaks	HIGH	Unbounded KeepAlive caching can cause severe memory issues, especially with large or numerous components	gotcha	vue3 keepalive memory-leak performance cache max-prop

KeepAlive Memory Management - Prevent Memory Leaks

Impact: HIGH - KeepAlive caches component instances in memory. Without proper limits and cleanup, this can lead to memory exhaustion, especially in applications with many routes or large component trees.

Task Checklist

• Always use the max prop to limit cached instances
• Clean up resources in onDeactivated hook
• Monitor memory usage when using KeepAlive extensively
• Be cautious with KeepAlive on memory-heavy components
• Test on memory-constrained devices (mobile, low-spec laptops)

The Problem: Unbounded Cache Growth

<template>
  <!-- DANGEROUS: No limit on cached components -->
  <KeepAlive>
    <component :is="currentView" />
  </KeepAlive>
</template>

When users navigate through many different components, each instance stays in memory:

• Chrome memory grows continuously
• VueComponent count keeps increasing
• App becomes sluggish or crashes

Solution: Set Cache Limits

<template>
  <!-- LRU cache: keeps max 10, evicts least recently used -->
  <KeepAlive :max="10">
    <component :is="currentView" />
  </KeepAlive>
</template>

How max works:

• KeepAlive uses an LRU (Least Recently Used) cache algorithm
• When cache exceeds max, the oldest unused component is destroyed
• This caps memory usage to a predictable maximum

Choose max Based on Your Use Case

<template>
  <!-- Tab-based UI: usually 3-5 tabs max -->
  <KeepAlive :max="5">
    <component :is="currentTab" />
  </KeepAlive>

  <!-- Route-based caching: limit to frequently visited pages -->
  <router-view v-slot="{ Component }">
    <KeepAlive :max="3" include="Dashboard,Settings,Profile">
      <component :is="Component" />
    </KeepAlive>
  </router-view>
</template>

Clean Up Resources in Deactivated Hook

Even with max, cached components hold resources. Clean up when deactivated:

<script setup>
import { ref, onActivated, onDeactivated, onUnmounted } from 'vue'

const chartInstance = ref(null)
const websocket = ref(null)
const intervalId = ref(null)

onActivated(() => {
  // Resume or recreate resources
  websocket.value = new WebSocket('...')
  intervalId.value = setInterval(fetchData, 5000)
})

onDeactivated(() => {
  // IMPORTANT: Clean up to reduce memory footprint while cached
  chartInstance.value?.destroy()
  chartInstance.value = null

  websocket.value?.close()
  websocket.value = null

  clearInterval(intervalId.value)
  intervalId.value = null
})

// Final cleanup when truly destroyed
onUnmounted(() => {
  // Same cleanup for when component is evicted from cache
  chartInstance.value?.destroy()
  websocket.value?.close()
  clearInterval(intervalId.value)
})
</script>

Third-Party Library Cleanup

Libraries that manipulate the DOM outside Vue need explicit cleanup:

<script setup>
import { ref, onMounted, onDeactivated, onUnmounted } from 'vue'

const mapContainer = ref(null)
let mapInstance = null

onMounted(() => {
  mapInstance = new MapLibrary(mapContainer.value)
})

onDeactivated(() => {
  // Some map libraries hold significant memory
  // Destroy and recreate on reactivation if needed
  mapInstance?.remove()
  mapInstance = null
})

onUnmounted(() => {
  mapInstance?.remove()
  mapInstance = null
})
</script>

Avoid KeepAlive for Memory-Heavy Components

Some components should NOT be cached:

<script setup>
const heavyComponents = ['VideoPlayer', 'LargeDataGrid', 'MapView']
</script>

<template>
  <!-- Exclude memory-heavy components from cache -->
  <KeepAlive :exclude="heavyComponents" :max="5">
    <component :is="currentView" />
  </KeepAlive>
</template>

Monitor Memory in Development

<script setup>
import { onActivated, onDeactivated } from 'vue'

if (import.meta.env.DEV) {
  onActivated(() => {
    console.log('Activated - Memory:', performance.memory?.usedJSHeapSize)
  })

  onDeactivated(() => {
    console.log('Deactivated - Memory:', performance.memory?.usedJSHeapSize)
  })
}
</script>

Key Points

1. Always set max - Never use KeepAlive without a reasonable limit
2. Clean up in onDeactivated - Don't wait for unmount to release resources
3. Exclude heavy components - Large data grids, media players, maps
4. Test on target devices - Mobile users have less memory
5. Monitor in development - Watch for growing memory usage

Reference

• Vue.js KeepAlive - Max Cached Instances
• Vue.js Avoiding Memory Leaks
• GitHub Issue: Memory leak with keep-alive