Reactivity API: Advanced
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Reactivity API: Advanced#
shallowRef()#
Shallow version of ref().
- Type
```ts
function shallowRef
interface ShallowRef
- Details
Unlike ref(), the inner value of a shallow ref is stored and exposed as-is, and will not be made deeply reactive. Only the .value access is reactive.
shallowRef() is typically used for performance optimizations of large data structures, or integration with external state management systems.
- Example
```js const state = shallowRef({ count: 1 })
// does NOT trigger change state.value.count = 2
// does trigger change state.value = { count: 2 } ```
- See also
- Guide - Reduce Reactivity Overhead for Large Immutable Structures
- Guide - Integration with External State Systems
triggerRef()#
Force trigger effects that depend on a shallow ref. This is typically used after making deep mutations to the inner value of a shallow ref.
- Type
ts
function triggerRef(ref: ShallowRef): void
- Example
```js const shallow = shallowRef({ greet: 'Hello, world' })
// Logs "Hello, world" once for the first run-through watchEffect(() => { console.log(shallow.value.greet) })
// This won't trigger the effect because the ref is shallow shallow.value.greet = 'Hello, universe'
// Logs "Hello, universe" triggerRef(shallow) ```
customRef()#
Creates a customized ref with explicit control over its dependency tracking and updates triggering.
- Type
```ts
function customRef
type CustomRefFactory
- Details
customRef() expects a factory function, which receives track and trigger functions as arguments and should return an object with get and set methods.
In general, track() should be called inside get(), and trigger() should be called inside set(). However, you have full control over when they should be called, or whether they should be called at all.
- Example
Creating a debounced ref that only updates the value after a certain timeout after the latest set call:
```js import { customRef } from 'vue'
export function useDebouncedRef(value, delay = 200) { let timeout return customRef((track, trigger) => { return { get() { track() return value }, set(newValue) { clearTimeout(timeout) timeout = setTimeout(() => { value = newValue trigger() }, delay) } } }) } ```
Usage in component:
```vue
```
:::warning Use with caution When using customRef, we should be cautious about the return value of its getter, particularly when generating new object datatypes each time the getter is run. This affects the relationship between parent and child components, where such a customRef has been passed as a prop.
The parent component's render function could be triggered by changes to a different reactive state. During rerender, the value of our customRef is reevaluated, returning a new object datatype as a prop to a child component. This prop is compared with its last value in the child component, and since they are different, the reactive dependencies of the customRef are triggered in the child component. Meanwhile, the reactive dependencies in the parent component do not run because the customRef's setter was not called, and its dependencies were not triggered as a result.
:::
shallowReactive()#
Shallow version of reactive().
- Type
ts
function shallowReactive<T extends object>(target: T): T
- Details
Unlike reactive(), there is no deep conversion: only root-level properties are reactive for a shallow reactive object. Property values are stored and exposed as-is - this also means properties with ref values will not be automatically unwrapped.
:::warning Use with Caution Shallow data structures should only be used for root level state in a component. Avoid nesting it inside a deep reactive object as it creates a tree with inconsistent reactivity behavior which can be difficult to understand and debug. :::
- Example
```js const state = shallowReactive({ foo: 1, nested: { bar: 2 } })
// mutating state's own properties is reactive state.foo++
// ...but does not convert nested objects isReactive(state.nested) // false
// NOT reactive state.nested.bar++ ```
shallowReadonly()#
Shallow version of readonly().
- Type
ts
function shallowReadonly<T extends object>(target: T): Readonly<T>
- Details
Unlike readonly(), there is no deep conversion: only root-level properties are made readonly. Property values are stored and exposed as-is - this also means properties with ref values will not be automatically unwrapped.
:::warning Use with Caution Shallow data structures should only be used for root level state in a component. Avoid nesting it inside a deep reactive object as it creates a tree with inconsistent reactivity behavior which can be difficult to understand and debug. :::
- Example
```js const state = shallowReadonly({ foo: 1, nested: { bar: 2 } })
// mutating state's own properties will fail state.foo++
// ...but works on nested objects isReadonly(state.nested) // false
// works state.nested.bar++ ```
toRaw()#
Returns the raw, original object of a Vue-created proxy.
- Type
ts
function toRaw<T>(proxy: T): T
- Details
toRaw() can return the original object from proxies created by reactive(), readonly(), shallowReactive() or shallowReadonly().
This is an escape hatch that can be used to temporarily read without incurring proxy access / tracking overhead or write without triggering changes. It is not recommended to hold a persistent reference to the original object. Use with caution.
- Example
```js const foo = {} const reactiveFoo = reactive(foo)
console.log(toRaw(reactiveFoo) === foo) // true ```
markRaw()#
Marks an object so that it will never be converted to a proxy. Returns the object itself.
- Type
ts
function markRaw<T extends object>(value: T): T
- Example
```js const foo = markRaw({}) console.log(isReactive(reactive(foo))) // false
// also works when nested inside other reactive objects const bar = reactive({ foo }) console.log(isReactive(bar.foo)) // false ```
:::warning Use with Caution
markRaw() and shallow APIs such as shallowReactive() allow you to selectively opt-out of the default deep reactive/readonly conversion and embed raw, non-proxied objects in your state graph. They can be used for various reasons:
-
Some values simply should not be made reactive, for example a complex 3rd party class instance, or a Vue component object.
-
Skipping proxy conversion can provide performance improvements when rendering large lists with immutable data sources.
They are considered advanced because the raw opt-out is only at the root level, so if you set a nested, non-marked raw object into a reactive object and then access it again, you get the proxied version back. This can lead to identity hazards - i.e. performing an operation that relies on object identity but using both the raw and the proxied version of the same object:
```js const foo = markRaw({ nested: {} })
const bar = reactive({
// although foo is marked as raw, foo.nested is not.
nested: foo.nested
})
console.log(foo.nested === bar.nested) // false ```
Identity hazards are in general rare. However, to properly utilize these APIs while safely avoiding identity hazards requires a solid understanding of how the reactivity system works.
:::
effectScope()#
Creates an effect scope object which can capture the reactive effects (i.e. computed and watchers) created within it so that these effects can be disposed together. For detailed use cases of this API, please consult its corresponding RFC.
- Type
```ts function effectScope(detached?: boolean): EffectScope
interface EffectScope {
run
- Example
```js const scope = effectScope()
scope.run(() => { const doubled = computed(() => counter.value * 2)
watch(doubled, () => console.log(doubled.value))
watchEffect(() => console.log('Count: ', doubled.value))
})
// to dispose all effects in the scope scope.stop() ```
getCurrentScope()#
Returns the current active effect scope if there is one.
- Type
ts
function getCurrentScope(): EffectScope | undefined
onScopeDispose()#
Registers a dispose callback on the current active effect scope. The callback will be invoked when the associated effect scope is stopped.
This method can be used as a non-component-coupled replacement of onUnmounted in reusable composition functions, since each Vue component's setup() function is also invoked in an effect scope.
A warning will be thrown if this function is called without an active effect scope. In 3.5+, this warning can be suppressed by passing true as the second argument.
- Type
ts
function onScopeDispose(fn: () => void, failSilently?: boolean): void