Lightning Web Components use the standard web component model, which includes the concept of Shadow DOM. Shadow DOM is a mechanism that isolates the component's internal DOM from the rest of the page, creating a boundary that prevents the component from accessing or being affected by the elements outside of its own subtree. However, this also means that events that are fired from within the component's shadow DOM do not propagate to the parent or ancestor components by default, unless they are configured to do so.
To configure how an event propagates, the component that dispatches the event can set two properties on the custom event object: bubbles and composed. The bubbles property determines whether the event can bubble up the containment hierarchy, which is the tree of components that contains the event source. The composed property determines whether the event can cross the shadow boundary, which is the boundary between the component's shadow DOM and the light DOM of its parent component.
The possible values and effects of these properties are:
* bubbles: true, composed: true: The event can bubble up the containment hierarchy and cross the shadow boundary. This means that the event can be handled by any component that is an ancestor of the event source, regardless of whether it is in the same shadow DOM or not. This is the most common setting for custom events that need to communicate with other components in the page.
* bubbles: true, composed: false: The event can bubble up the containment hierarchy, but cannot cross the shadow boundary. This means that the event can be handled by any component that is an ancestor of the event source, as long as it is in the same shadow DOM. This is useful for custom events that need to
* communicate with other components within the same shadow tree, but not outside of it.
* bubbles: false, composed: true: The event cannot bubble up the containment hierarchy, but can cross the shadow boundary. This means that the event can be handled only by the component that dispatched the event, or by the component that contains the event source in its light DOM. This is useful for custom events that need to communicate with the direct parent component, but not with any other ancestor components.
* bubbles: false, composed: false: The event cannot bubble up the containment hierarchy, nor can it cross the shadow boundary. This means that the event can be handled only by the component that dispatched the event. This is useful for custom events that do not need to communicate with any other components, but only with the event source itself.
Therefore, the correct answer is B. bubbles: true, composed: true, as this is the only setting that enables the event to bubble up the containment hierarchy and cross the shadow boundary.
References:
* Configure Event Propagation
* Handle Events