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Base element class which manages element properties and attributes. When properties change, the update method is asynchronously called. This method should be supplied by subclassers to render updates as desired.

Hierarchy

Index

Constructors

constructor

Properties

Static Protected finalized

finalized: boolean = true

Marks class as having finished creating properties.

Static properties

User-supplied object that maps property names to PropertyDeclaration objects containing options for configuring the property.

Accessors

Protected hasUpdated

  • get hasUpdated(): number

updateComplete

  • get updateComplete(): Promise<unknown>
  • Returns a Promise that resolves when the element has completed updating. The Promise value is a boolean that is true if the element completed the update without triggering another update. The Promise result is false if a property was set inside updated(). This getter can be implemented to await additional state. For example, it is sometimes useful to await a rendered element before fulfilling this Promise. To do this, first await super.updateComplete then any subsequent state.

    Returns Promise<unknown>

    The Promise returns a boolean that indicates if the update resolved without triggering another update.

Static observedAttributes

  • get observedAttributes(): string[]
  • Returns a list of attributes corresponding to the registered properties.

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    Returns string[]

Methods

attributeChangedCallback

  • attributeChangedCallback(name: string, old: string, value: string): void
  • Synchronizes property values when attributes change.

    Parameters

    • name: string
    • old: string
    • value: string

    Returns void

connectedCallback

  • connectedCallback(): void

disconnectedCallback

  • disconnectedCallback(): void
  • Allows for super.disconnectedCallback() in extensions while reserving the possibility of making non-breaking feature additions when disconnecting at some point in the future.

    Returns void

Protected firstUpdated

  • Invoked when the element is first updated. Implement to perform one time work on the element after update.

    Setting properties inside this method will trigger the element to update again after this update cycle completes.

    • @param _changedProperties Map of changed properties with old values

    Parameters

    Returns void

Protected initialize

  • initialize(): void
  • Performs element initialization. By default captures any pre-set values for registered properties.

    Returns void

Protected performUpdate

  • performUpdate(): void | Promise<unknown>
  • Performs an element update.

    You can override this method to change the timing of updates. For instance, to schedule updates to occur just before the next frame:

    protected async performUpdate(): Promise<unknown> {
      await new Promise((resolve) => requestAnimationFrame(() => resolve()));
      super.performUpdate();
    }

    Returns void | Promise<unknown>

requestUpdate

  • requestUpdate(name?: PropertyKey, oldValue?: any): Promise<unknown>
  • Requests an update which is processed asynchronously. This should be called when an element should update based on some state not triggered by setting a property. In this case, pass no arguments. It should also be called when manually implementing a property setter. In this case, pass the property name and oldValue to ensure that any configured property options are honored. Returns the updateComplete Promise which is resolved when the update completes.

    Parameters

    • Optional name: PropertyKey

      (optional) name of requesting property

    • Optional oldValue: any

      (optional) old value of requesting property

    Returns Promise<unknown>

    A Promise that is resolved when the update completes.

Protected shouldUpdate

  • Controls whether or not update should be called when the element requests an update. By default, this method always returns true, but this can be customized to control when to update.

    • @param _changedProperties Map of changed properties with old values

    Parameters

    Returns boolean

Protected update

  • Updates the element. This method reflects property values to attributes. It can be overridden to render and keep updated element DOM. Setting properties inside this method will not trigger another update.

    • @param _changedProperties Map of changed properties with old values

    Parameters

    Returns void

Protected updated

  • Invoked whenever the element is updated. Implement to perform post-updating tasks via DOM APIs, for example, focusing an element.

    Setting properties inside this method will trigger the element to update again after this update cycle completes.

    • @param _changedProperties Map of changed properties with old values

    Parameters

    Returns void

Static createProperty

  • Creates a property accessor on the element prototype if one does not exist. The property setter calls the property's hasChanged property option or uses a strict identity check to determine whether or not to request an update.

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    Parameters

    Returns void

Static Protected finalize

  • finalize(): void
  • Creates property accessors for registered properties and ensures any superclasses are also finalized.

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    Returns void

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