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.
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.
详情
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.
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:
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. It can be overridden to render and keep updated element DOM. 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(...).
参数
name
PropertyKey
详情
Note, this method should be considered "final" and not overridden. To customize the options for a given property, override createProperty.
Indicates how and whether the property becomes an observed attribute. If the value is false, the property is not added to observedAttributes. If true or absent, the lowercased property name is observed (e.g. fooBar becomes foobar). If a string, the string value is observed (e.g attribute: 'foo-bar').
Indicates how to convert the attribute to/from a property. If this value is a function, it is used to convert the attribute value a the property value. If it's an object, it can have keys for fromAttribute and toAttribute. If no toAttribute function is provided and reflect is set to true, the property value is set directly to the attribute. A default converter is used if none is provided; it supports Boolean, String, Number, Object, and Array. Note, when a property changes and the converter is used to update the attribute, the property is never updated again as a result of the attribute changing, and vice versa.
Indicates whether an accessor will be created for this property. By default, an accessor will be generated for this property that requests an update when set. If this flag is true, no accessor will be created, and it will be the user's responsibility to call this.requestUpdate(propertyName, oldValue) to request an update when the property changes.
Indicates if the property should reflect to an attribute. If true, when the property is set, the attribute is set using the attribute name determined according to the rules for the attribute property option and the value of the property converted using the rules from the converter property option.
A function that indicates if a property should be considered changed when it is set. The function should take the newValue and oldValue and return true if an update should be requested.
Map of properties to PropertyDeclaration options. For each property an accessor is made, and the property is processed according to the PropertyDeclaration options.