Understanding Reference Sharing in Vue 3 Reactivity

When working with Vue 3's Composition API, assigning a reactive reference to another variable often leads to unintended state mutations. Because JavaScript objects and arrays are passed by reference, both variables point to the same memory address. Altering one automatically propagates to the other, which can compromise component state isolation.

const sourceConfig = ref({ theme: 'dark', fontSize: 14 })
const derivedConfig = sourceConfig

derivedConfig.value.theme = 'light'
console.log(sourceConfig.value.theme) // Outputs: 'light'

Duplicating Flat Objects

To prevent cross-contamination between flat data structures, you must allocate a new memory address. Several native and third-party approaches achieve this:

1. Spread Syntax

Using the rest/spread operator extracts top-level keys in to a fresh object literal, effectively breaking the reference chain at the first level.

const sourceConfig = ref({ theme: 'dark', fontSize: 14 })
const derivedConfig = ref({ ...sourceConfig.value })

derivedConfig.value.theme = 'light'
// sourceConfig remains unchanged

2. Object.assign()

This built-in method copies enumerable own properties from source objects to a target object. Passing an empty object as the target ensures a distinct reference is generated.

const sourceConfig = ref({ theme: 'dark', fontSize: 14 })
const derivedConfig = ref(Object.assign({}, sourceConfig.value))

derivedConfig.value.theme = 'light'

3. Utility Libraries (Lodash)

Third-party utilities like Lodash provide dedicated cloning functions. Ensure the package is installed via your preferred package manager (npm i lodash-es or yarn add lodash-es) before importing.

import { clone } from 'lodash-es'

const sourceConfig = ref({ theme: 'dark', fontSize: 14 })
const derivedConfig = ref(clone(sourceConfig.value))

derivedConfig.value.theme = 'light'

Handling Arrays and Mixed Structures

Shallow copying arrays with \[...array\] or Array.from() only duplicates the array wrapper. The inner objects remain linked to the original references. Mutating nested properties will still propagate back to the source.

const primaryDataset = ref([
  { id: 101, label: 'Metric A', threshold: 50 },
  { id: 102, label: 'Metric B', threshold: 120 }
])

const secondaryDataset = ref([...primaryDataset.value])
secondaryDataset.value[0].label = 'Updated A'
// primaryDataset.value[0].label is now 'Updated A'

To fully isolate array data, apply copying strategies at the element level:

1. Element-wise Mapping

Iterate through the array and spread each nested object individually to guarantee independent references.

const secondaryDataset = ref(primaryDataset.value.map(item => ({ ...item })))
secondaryDataset.value[0].label = 'Updated A'

2. Serialization Round-Trip

Stringifying and parsing the entire structure forces JavaScript to reconstruct every object and array from scratch, effectively breaking all internal references.

const secondaryDataset = ref(JSON.parse(JSON.stringify(primaryDataset.value)))
secondaryDataset.value[0].label = 'Updated A'

3. Deep Cloning Utilities

Lodash's deep cloning function handles recursive traversal safely, including circular references and non-enumerable properties that JSON serialization might miss.

import { cloneDeep } from 'lodash-es'

const secondaryDataset = ref(cloneDeep(primaryDataset.value))
secondaryDataset.value[0].label = 'Updated A'

Isolating Primitive Arrays

For arrays containing only primitive values (numbers, strings, booleans), standard array duplication methods work reliably since primitives are copied by value.

const initialMetrics = ref([10, 25, 40, 55])
const workingMetrics = ref(Array.from(initialMetrics.value))

workingMetrics.value[1] = 999
// initialMetrics remains [10, 25, 40, 55]

Managing Deeply Nested Hierarchies

Shallow copying techniques fail when data contains multiple levels of nesting. Modifying a property deep within the hierarchy will traverse back through the shared reference chain.

const sourceHierarchy = ref({
  user: {
    profile: {
      displayName: 'Developer_X'
    }
  },
  role: 'admin'
})

const targetHierarchy = ref({ ...sourceHierarchy.value })
targetHierarchy.value.user.profile.displayName = 'Admin_Z'
// sourceHierarchy is inadvertently mutated

Resolving this requires full structural duplication. Both serialization and dedicated deep-cloning libraries remain the most reliable approaches:

// Approach 1: Native serialization
const targetHierarchy = ref(JSON.parse(JSON.stringify(sourceHierarchy.value)))

// Approach 2: Lodash deep clone
import { cloneDeep } from 'lodash-es'
const targetHierarchy = ref(cloneDeep(sourceHierarchy.value))

targetHierarchy.value.user.profile.displayName = 'Admin_Z'
// sourceHierarchy stays intact

Standard shallow cloning functions will not resolve multi-level nesting. Always verify the depth of your data structure before selecting a duplication strategy to ensure Vue's reactivity system tracks the correct reference.