Vue Reactivity Loss

In this tutorial, you'll learn about Vue Reactivity Loss Fix. We cover key concepts, practical examples, and best practices.

The Problem

Changing a variable does not update the UI in Vue 3.

Wrong

<script setup>
let count = 0

function increment() {
  count++ // UI does not update
}
</script>

<template>
  <p>{{ count }}</p>
  <button @click="increment">+1</button>
</template>

Output: clicking the button increments count in memory, but the UI stays at 0.

Right

Use ref() or reactive():

<script setup>
import { ref } from 'vue'

const count = ref(0)

function increment() {
  count.value++
}
</script>

<template>
  <p>{{ count }}</p>
  <button @click="increment">+1</button>
</template>

Expected output: clicking the button updates {{ count }} from 0 to 1, 2, 3, etc.

Prevention

• Always use ref() for primitive values and reactive() for objects
• Access ref values with .value in JavaScript (auto-unwrapped in templates)
• Do not destructure reactive objects (use toRefs() if needed)

Common Mistakes with reactivity loss

1. Forgetting deriving (Show, Eq) on custom data types needed for debugging
2. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
3. Using head and tail instead of pattern matching, causing runtime errors on empty lists

These mistakes appear frequently in real-world VUE code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ