title: Create Stateful Methods in Lifecycle Hooks impact: MEDIUM impactDescription: Stateful functions like debounce/throttle in methods are shared across all component instances type: capability tags: [vue3, options-api, debounce, throttle, lifecycle, cleanup]

Create Stateful Methods in Lifecycle Hooks

Impact: MEDIUM - If you define debounced, throttled, or other stateful functions directly in the methods option, all instances of the component share the same function state. This causes race conditions and bugs in lists of components.

When a component is reused (e.g., in v-for), each instance needs its own debounced/throttled function. Define these in the created() hook and clean them up in unmounted() to prevent memory leaks.

Task Checklist

• Never define debounced/throttled functions directly in methods
• Create stateful functions in created() lifecycle hook
• Always clean up (cancel timers) in unmounted()

Incorrect:

import { debounce } from 'lodash-es'

export default {
  methods: {
    // WRONG: All component instances share this debounced function!
    // If used in a v-for, clicking one button affects all instances
    handleClick: debounce(function() {
      this.performSearch()
    }, 500)
  }
}

Correct:

import { debounce } from 'lodash-es'

export default {
  created() {
    // CORRECT: Each instance gets its own debounced function
    this.debouncedSearch = debounce(this.performSearch, 500)
  },
  unmounted() {
    // CORRECT: Clean up to prevent memory leaks and stale calls
    this.debouncedSearch.cancel()
  },
  methods: {
    handleClick() {
      this.debouncedSearch()
    },
    performSearch() {
      // Actual search logic
    }
  }
}

Reference

• Vue.js Reactivity Fundamentals - Stateful Methods