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Component Instance

INFO

This page documents the built-in properties and methods exposed on the component public instance, i.e. this.

All properties listed on this page are readonly (except nested properties in $data).

$data

The object returned from the data option, made reactive by the component. The component instance proxies access to the properties on its data object.

  • Type

    ts
    interface ComponentPublicInstance {
      $data: object
    }

$props

An object representing the component's current, resolved props.

  • Type

    ts
    interface ComponentPublicInstance {
      $props: object
    }
  • Details

    Only props declared via the props option will be included. The component instance proxies access to the properties on its props object.

$el

The root DOM node that the component instance is managing.

  • Type

    ts
    interface ComponentPublicInstance {
      $el: Node | undefined
    }
  • Details

    $el will be undefined until the component is mounted.

    • For components with a single root element, $el will point to that element.
    • For components with text root, $el will point to the text node.
    • For components with multiple root nodes, $el will be the placeholder DOM node that Vue uses to keep track of the component's position in the DOM (a text node, or a comment node in SSR hydration mode).

    TIP

    For consistency, it is recommended to use template refs for direct access to elements instead of relying on $el.

$options

The resolved component options used for instantiating the current component instance.

  • Type

    ts
    interface ComponentPublicInstance {
      $options: ComponentOptions
    }
  • Details

    The $options object exposes the resolved options for the current component and is the merge result of these possible sources:

    • Global mixins
    • Component extends base
    • Component mixins

    It is typically used to support custom component options:

    js
    const app = createApp({
      customOption: 'foo',
      created() {
        console.log(this.$options.customOption) // => 'foo'
      }
    })
  • See also app.config.optionMergeStrategies

$parent

The parent instance, if the current instance has one. It will be null for the root instance itself.

  • Type

    ts
    interface ComponentPublicInstance {
      $parent: ComponentPublicInstance | null
    }

$root

The root component instance of the current component tree. If the current instance has no parents this value will be itself.

  • Type

    ts
    interface ComponentPublicInstance {
      $root: ComponentPublicInstance
    }

$slots

An object representing the slots passed by the parent component.

  • Type

    ts
    interface ComponentPublicInstance {
      $slots: { [name: string]: Slot }
    }
    
    type Slot = (...args: any[]) => VNode[]
  • Details

    Typically used when manually authoring render functions, but can also be used to detect whether a slot is present.

    Each slot is exposed on this.$slots as a function that returns an array of vnodes under the key corresponding to that slot's name. The default slot is exposed as this.$slots.default.

    If a slot is a scoped slot, arguments passed to the slot functions are available to the slot as its slot props.

  • See also Render Functions - Rendering Slots

$refs

An object of DOM elements and component instances, registered via template refs.

$attrs

An object that contains the component's fallthrough attributes.

  • Type

    ts
    interface ComponentPublicInstance {
      $attrs: object
    }
  • Details

    Fallthrough Attributes are attributes and event handlers passed by the parent component, but not declared as a prop or an emitted event by the child.

    By default, everything in $attrs will be automatically inherited on the component's root element if there is only a single root element. This behavior is disabled if the component has multiple root nodes, and can be explicitly disabled with the inheritAttrs option.

  • See also

$watch()

Imperative API for creating watchers.

  • Type

    ts
    interface ComponentPublicInstance {
      $watch(
        source: string | (() => any),
        callback: WatchCallback,
        options?: WatchOptions
      ): StopHandle
    }
    
    type WatchCallback<T> = (
      value: T,
      oldValue: T,
      onCleanup: (cleanupFn: () => void) => void
    ) => void
    
    interface WatchOptions {
      immediate?: boolean // default: false
      deep?: boolean // default: false
      flush?: 'pre' | 'post' | 'sync' // default: 'pre'
      onTrack?: (event: DebuggerEvent) => void
      onTrigger?: (event: DebuggerEvent) => void
    }
    
    type StopHandle = () => void
  • Details

    The first argument is the watch source. It can be a component property name string, a simple dot-delimited path string, or a getter function.

    The second argument is the callback function. The callback receives the new value and the old value of the watched source.

    • immediate: trigger the callback immediately on watcher creation. Old value will be undefined on the first call.
    • deep: force deep traversal of the source if it is an object, so that the callback fires on deep mutations. See Deep Watchers.
    • flush: adjust the callback's flush timing. See Callback Flush Timing and watchEffect().
    • onTrack / onTrigger: debug the watcher's dependencies. See Watcher Debugging.
  • Example

    Watch a property name:

    js
    this.$watch('a', (newVal, oldVal) => {})

    Watch a dot-delimited path:

    js
    this.$watch('a.b', (newVal, oldVal) => {})

    Using getter for more complex expressions:

    js
    this.$watch(
      // every time the expression `this.a + this.b` yields
      // a different result, the handler will be called.
      // It's as if we were watching a computed property
      // without defining the computed property itself.
      () => this.a + this.b,
      (newVal, oldVal) => {}
    )

    Stopping the watcher:

    js
    const unwatch = this.$watch('a', cb)
    
    // later...
    unwatch()
  • See also

$emit()

Trigger a custom event on the current instance. Any additional arguments will be passed into the listener's callback function.

  • Type

    ts
    interface ComponentPublicInstance {
      $emit(event: string, ...args: any[]): void
    }
  • Example

    js
    export default {
      created() {
        // only event
        this.$emit('foo')
        // with additional arguments
        this.$emit('bar', 1, 2, 3)
      }
    }
  • See also

$forceUpdate()

Force the component instance to re-render.

  • Type

    ts
    interface ComponentPublicInstance {
      $forceUpdate(): void
    }
  • Details

    This should be rarely needed given Vue's fully automatic reactivity system. The only cases where you may need it is when you have explicitly created non-reactive component state using advanced reactivity APIs.

$nextTick()

Instance-bound version of the global nextTick().

  • Type

    ts
    interface ComponentPublicInstance {
      $nextTick(callback?: (this: ComponentPublicInstance) => void): Promise<void>
    }
  • Details

    The only difference from the global version of nextTick() is that the callback passed to this.$nextTick() will have its this context bound to the current component instance.

  • See also nextTick()

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