agent-skills/skills/vue-best-practices/reference/reactivity-proxy-identity-hazard.md

title, impact, impactDescription, type, tags

title	impact	impactDescription	type	tags
Avoid Comparing Reactive Objects with === Operator	HIGH	Reactive proxies have different identity than original objects - comparison bugs are silent and hard to debug	gotcha	vue3 reactivity proxy comparison debugging identity

Avoid Comparing Reactive Objects with === Operator

Impact: HIGH - Vue's reactive() returns a Proxy wrapper that has a different identity than the original object. Using === to compare reactive objects can lead to silent bugs where comparisons unexpectedly return false.

When you wrap an object with reactive(), the returned proxy is NOT equal to the original object. Additionally, accessing nested objects from a reactive object returns new proxy wrappers each time, which can cause identity comparison issues.

Task Checklist

• Never compare reactive object instances with === directly
• Use unique identifiers (ID, UUID) for object comparison instead
• Use toRaw() on both sides when identity comparison is absolutely necessary
• Consider using primitive identifiers from database records for comparison

Incorrect:

import { reactive } from 'vue'

const original = { id: 1, name: 'Item' }
const state = reactive(original)

// BUG: Always returns false - proxy !== original
if (state === original) {
  console.log('Same object') // Never executes
}

// BUG: Nested object comparison fails
const items = reactive([{ id: 1 }, { id: 2 }])
const item = items[0]

// Later...
if (items[0] === item) {
  // May or may not work depending on Vue's proxy caching
}

// BUG: Comparing items from different reactive sources
const listA = reactive([{ id: 1 }])
const listB = reactive([{ id: 1 }])
if (listA[0] === listB[0]) {
  // Never true, even though they represent the same data
}

Correct:

import { reactive, toRaw } from 'vue'

const original = { id: 1, name: 'Item' }
const state = reactive(original)

// CORRECT: Use toRaw() for identity comparison
if (toRaw(state) === original) {
  console.log('Same underlying object') // Works!
}

// BEST: Use unique identifiers instead
const items = reactive([
  { id: 'uuid-1', name: 'Item 1' },
  { id: 'uuid-2', name: 'Item 2' }
])

function findItem(targetId) {
  return items.find(item => item.id === targetId)
}

function isSelected(item) {
  return selectedId.value === item.id // Compare IDs, not objects
}

// CORRECT: For Set/Map operations, use primitive keys
const selectedIds = reactive(new Set())
selectedIds.add(item.id)  // Use ID, not object
selectedIds.has(item.id)  // Check by ID

// When you must compare objects, use toRaw on both sides
import { toRaw, isReactive } from 'vue'

function areEqual(a, b) {
  const rawA = isReactive(a) ? toRaw(a) : a
  const rawB = isReactive(b) ? toRaw(b) : b
  return rawA === rawB
}

Reference

• Vue.js Reactivity in Depth
• Vue.js toRaw() API