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Quiz

Test your knowledge: HTML Custom Elements

Checkpoint on custom-element naming, registration, upgrades, lifecycle callbacks, observed attributes, and native-versus-custom semantics.

8 questions ~8 min Advanced

Knowledge check

Test your knowledge: HTML Custom Elements

Checkpoint on custom-element naming, registration, upgrades, lifecycle callbacks, observed attributes, and native-versus-custom semantics.

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Which is a valid autonomous custom-element name?

Autonomous custom-element names must follow the valid custom element name rules, including containing a hyphen.
Which call registers an autonomous custom element?

CustomElementRegistry.define() associates the valid name with the constructor.
Which callback is intended for work that depends on the element being connected?

connectedCallback() is invoked when the custom element is connected.
What does static observedAttributes control?

Only observed attribute changes are delivered through attributeChangedCallback().
What must happen before using this in a custom-element constructor?

The HTMLElement base constructor must run first through super().
What can happen when a definition is registered after matching markup already exists?

The custom-element upgrade machinery can upgrade existing matching elements after definition.
Which syntax identifies a customized built-in element in markup?

Customized built-in elements retain the built-in local name and use the is attribute.
What should an author assume about an autonomous custom element’s semantics?

Autonomous custom elements do not acquire the semantics of an existing native element merely by being registered.