title: Simple Hash Routing Requires Event Listener Cleanup impact: MEDIUM impactDescription: When implementing basic routing without Vue Router, forgetting to remove hashchange listeners causes memory leaks and multiple handler execution type: gotcha tags: [vue3, routing, events, memory-leak, cleanup]

Simple Hash Routing Requires Event Listener Cleanup

Impact: MEDIUM - When implementing basic client-side routing without Vue Router (using hash-based routing with hashchange events), you must clean up event listeners when the component unmounts. Failure to do so causes memory leaks and can result in multiple handlers firing after the component is recreated.

Task Checklist

• Store event listener reference for cleanup
• Use onUnmounted to remove event listener
• Consider using Vue Router instead for production apps
• Test component mount/unmount cycles

The Problem

<script setup>
import { ref, computed } from 'vue'
import Home from './Home.vue'
import About from './About.vue'

const routes = {
  '/': Home,
  '/about': About
}

const currentPath = ref(window.location.hash)

// BUG: Event listener is never removed!
// Each time this component mounts, a NEW listener is added
// After mounting 5 times, you have 5 listeners running
window.addEventListener('hashchange', () => {
  currentPath.value = window.location.hash
})

const currentView = computed(() => {
  return routes[currentPath.value.slice(1) || '/']
})
</script>

What happens:

1. Component mounts, adds listener
2. Component unmounts (e.g., route change, v-if toggle)
3. Component mounts again, adds ANOTHER listener
4. Now TWO listeners respond to each hash change
5. Eventually causes performance issues and memory leaks

Solution: Proper Cleanup with onUnmounted

<script setup>
import { ref, computed, onUnmounted } from 'vue'
import Home from './Home.vue'
import About from './About.vue'
import NotFound from './NotFound.vue'

const routes = {
  '/': Home,
  '/about': About
}

const currentPath = ref(window.location.hash)

// Store handler reference for cleanup
function handleHashChange() {
  currentPath.value = window.location.hash
}

// Add listener
window.addEventListener('hashchange', handleHashChange)

// CRITICAL: Remove listener on unmount
onUnmounted(() => {
  window.removeEventListener('hashchange', handleHashChange)
})

const currentView = computed(() => {
  return routes[currentPath.value.slice(1) || '/'] || NotFound
})
</script>

Solution: Using Options API

<script>
import Home from './Home.vue'
import About from './About.vue'
import NotFound from './NotFound.vue'

const routes = {
  '/': Home,
  '/about': About
}

export default {
  data() {
    return {
      currentPath: window.location.hash
    }
  },

  computed: {
    currentView() {
      return routes[this.currentPath.slice(1) || '/'] || NotFound
    }
  },

  mounted() {
    // Store bound handler for cleanup
    this.hashHandler = () => {
      this.currentPath = window.location.hash
    }
    window.addEventListener('hashchange', this.hashHandler)
  },

  beforeUnmount() {
    // Clean up
    window.removeEventListener('hashchange', this.hashHandler)
  }
}
</script>

Solution: Composable for Reusable Hash Routing

// composables/useHashRouter.js
import { ref, computed, onUnmounted } from 'vue'

export function useHashRouter(routes, notFoundComponent = null) {
  const currentPath = ref(window.location.hash)

  function handleHashChange() {
    currentPath.value = window.location.hash
  }

  // Setup
  window.addEventListener('hashchange', handleHashChange)

  // Cleanup - handled automatically when component unmounts
  onUnmounted(() => {
    window.removeEventListener('hashchange', handleHashChange)
  })

  const currentView = computed(() => {
    const path = currentPath.value.slice(1) || '/'
    return routes[path] || notFoundComponent
  })

  function navigate(path) {
    window.location.hash = path
  }

  return {
    currentPath,
    currentView,
    navigate
  }
}

<!-- Usage -->
<script setup>
import { useHashRouter } from '@/composables/useHashRouter'
import Home from './Home.vue'
import About from './About.vue'
import NotFound from './NotFound.vue'

const { currentView } = useHashRouter({
  '/': Home,
  '/about': About
}, NotFound)
</script>

<template>
  <component :is="currentView" />
</template>

When to Use Simple Routing vs Vue Router

Key Points

1. Always clean up event listeners - Use onUnmounted or beforeUnmount
2. Store handler reference - Anonymous functions can't be removed
3. Consider Vue Router for real apps - It handles cleanup automatically
4. Test unmount scenarios - v-if toggling, hot module replacement
5. Composables help encapsulate cleanup logic - Reusable and automatic

Reference

• Vue.js Routing Documentation
• Vue Router Official Library