Base element class that manages element properties and attributes, and renders a lit-html template.
Import
import { LitElement } from'lit-element';
Details
To define a component, subclass LitElement and implement a render method to provide the component's template. Define properties using the properties property or the property decorator.
Reference to the underlying library method used to render the element's DOM. By default, points to the render method from lit-html's shady-render module.
Details
Most users will never need to touch this property.
This property should not be confused with the render instance method, which should be overridden to define a template for the element.
Advanced users creating a new base class based on LitElement can override this property to point to a custom render method with a signature that matches shady-render's render method.
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(). If the Promise is rejected, an exception was thrown during the update.
Details
To await additional asynchronous work, override the _getUpdateComplete method. For example, it is sometimes useful to await a rendered element before fulfilling this Promise. To do this, first await super._getUpdateComplete(), then any subsequent state.
Applies styling to the element shadowRoot using the styles property. Styling will apply using shadowRoot.adoptedStyleSheets where available and will fallback otherwise. When Shadow DOM is polyfilled, ShadyCSS scopes styles and adds them to the document. When Shadow DOM is available but adoptedStyleSheets is not, styles are appended to the end of the shadowRoot to mimic spec behavior.
Returns the node into which the element should render and by default creates and returns an open shadowRoot. Implement to customize where the element's DOM is rendered. For example, to render into the element's childNodes, return this.
Allows for super.disconnectedCallback() in extensions while reserving the possibility of making non-breaking feature additions when disconnecting at some point in the future.
It is not safe to override the updateComplete getter directly due to a limitation in TypeScript which means it is not possible to call a superclass getter (e.g. super.updateComplete.then(...)) when the target language is ES5 (https://github.com/microsoft/TypeScript/issues/338). This method should be overridden instead. For example:
Performs element initialization. By default this calls createRenderRoot to create the element renderRoot node and captures any pre-set values for registered properties.
Invoked on each update to perform rendering tasks. This method may return any value renderable by lit-html's NodePart - typically a TemplateResult. Setting properties inside this method will not trigger the element to update.
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.
This protected version of requestUpdate does not access or return the updateComplete promise. This promise can be overridden and is therefore not free to access.
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.
Updates the element. This method reflects property values to attributes and calls render to render DOM via lit-html. Setting properties inside this method will not trigger another update.
Creates a property accessor on the element prototype if one does not exist and stores a PropertyDeclaration for the property with the given options. 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.
This method may be overridden to customize properties; however, when doing so, it's important to call super.createProperty to ensure the property is setup correctly. This method calls getPropertyDescriptor internally to get a descriptor to install. To customize what properties do when they are get or set, override getPropertyDescriptor. To customize the options for a property, implement createProperty like this:
Returns a property descriptor to be defined on the given named property. If no descriptor is returned, the property will not become an accessor. For example,
Returns the property options associated with the given property. These options are defined with a PropertyDeclaration via the properties object or the @property decorator and are registered in createProperty(...).
Parameters
name
PropertyKey
Details
Note, this method should be considered "final" and not overridden. To customize the options for a given property, override createProperty.