Reactivity API: Utilities | Vue.js

Reactivity API: Utilities
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isRef()
​

Checks if a value is a ref object.

Type

ts
function isRef<T>(r: Ref<T> | unknown): r is Ref<T>

Note the return type is a type predicate, which means isRef can be used as a type guard:

ts
let foo: unknown
if (isRef(foo)) {
  // foo's type is narrowed to Ref<unknown>
  foo.value
}
unref()
​

Returns the inner value if the argument is a ref, otherwise return the argument itself. This is a sugar function for val = isRef(val) ? val.value : val.

Type

ts
function unref<T>(ref: T | Ref<T>): T

Example

ts
function useFoo(x: number | Ref<number>) {
  const unwrapped = unref(x)
  // unwrapped is guaranteed to be number now
}
toRef()
​

Can be used to normalize values / refs / getters into refs (3.3+).

Can also be used to create a ref for a property on a source reactive object. The created ref is synced with its source property: mutating the source property will update the ref, and vice-versa.

Type

ts
// normalization signature (3.3+)
function toRef<T>(
  value: T
): T extends () => infer R
  ? Readonly<Ref<R>>
  : T extends Ref
  ? T
  : Ref<UnwrapRef<T>>

// object property signature
function toRef<T extends object, K extends keyof T>(
  object: T,
  key: K,
  defaultValue?: T[K]
): ToRef<T[K]>

type ToRef<T> = T extends Ref ? T : Ref<T>

Example

Normalization signature (3.3+):

js
// returns existing refs as-is
toRef(existingRef)

// creates a readonly ref that calls the getter on .value access
toRef(() => props.foo)

// creates normal refs from non-function values
// equivalent to ref(1)
toRef(1)

Object property signature:

js
const state = reactive({
  foo: 1,
  bar: 2
})

// a two-way ref that syncs with the original property
const fooRef = toRef(state, 'foo')

// mutating the ref updates the original
fooRef.value++
console.log(state.foo) // 2

// mutating the original also updates the ref
state.foo++
console.log(fooRef.value) // 3

Note this is different from:

js
const fooRef = ref(state.foo)

The above ref is not synced with state.foo, because the ref() receives a plain number value.

toRef() is useful when you want to pass the ref of a prop to a composable function:

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

const props = defineProps(/* ... */)

// convert `props.foo` into a ref, then pass into
// a composable
useSomeFeature(toRef(props, 'foo'))

// getter syntax - recommended in 3.3+
useSomeFeature(toRef(() => props.foo))
</script>

When toRef is used with component props, the usual restrictions around mutating the props still apply. Attempting to assign a new value to the ref is equivalent to trying to modify the prop directly and is not allowed. In that scenario you may want to consider using computed with get and set instead. See the guide to using v-model with components for more information.

When using the object property signature, toRef() will return a usable ref even if the source property doesn't currently exist. This makes it possible to work with optional properties, which wouldn't be picked up by toRefs.

toValue() 
​

Normalizes values / refs / getters to values. This is similar to unref(), except that it also normalizes getters. If the argument is a getter, it will be invoked and its return value will be returned.

This can be used in Composables to normalize an argument that can be either a value, a ref, or a getter.

Type

ts
function toValue<T>(source: T | Ref<T> | (() => T)): T

Example

js
toValue(1) //       --> 1
toValue(ref(1)) //  --> 1
toValue(() => 1) // --> 1

Normalizing arguments in composables:

ts
import type { MaybeRefOrGetter } from 'vue'

function useFeature(id: MaybeRefOrGetter<number>) {
  watch(() => toValue(id), id => {
    // react to id changes
  })
}

// this composable supports any of the following:
useFeature(1)
useFeature(ref(1))
useFeature(() => 1)
toRefs()
​

Converts a reactive object to a plain object where each property of the resulting object is a ref pointing to the corresponding property of the original object. Each individual ref is created using toRef().

Type

ts
function toRefs<T extends object>(
  object: T
): {
  [K in keyof T]: ToRef<T[K]>
}

type ToRef = T extends Ref ? T : Ref<T>

Example

js
const state = reactive({
  foo: 1,
  bar: 2
})

const stateAsRefs = toRefs(state)
/*
Type of stateAsRefs: {
  foo: Ref<number>,
  bar: Ref<number>
}
*/

// The ref and the original property is "linked"
state.foo++
console.log(stateAsRefs.foo.value) // 2

stateAsRefs.foo.value++
console.log(state.foo) // 3

toRefs is useful when returning a reactive object from a composable function so that the consuming component can destructure/spread the returned object without losing reactivity:

js
function useFeatureX() {
  const state = reactive({
    foo: 1,
    bar: 2
  })

  // ...logic operating on state

  // convert to refs when returning
  return toRefs(state)
}

// can destructure without losing reactivity
const { foo, bar } = useFeatureX()

toRefs will only generate refs for properties that are enumerable on the source object at call time. To create a ref for a property that may not exist yet, use toRef instead.

isProxy()
​

Checks if an object is a proxy created by reactive(), readonly(), shallowReactive() or shallowReadonly().

Type

ts
function isProxy(value: unknown): boolean
isReactive()
​

Checks if an object is a proxy created by reactive() or shallowReactive().

Type

ts
function isReactive(value: unknown): boolean
isReadonly()
​

Checks whether the passed value is a readonly object. The properties of a readonly object can change, but they can't be assigned directly via the passed object.

The proxies created by readonly() and shallowReadonly() are both considered readonly, as is a computed() ref without a set function.

Type

ts
function isReadonly(value: unknown): boolean