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rfc: introduce "connected" and "disconnected" lifecycle hooks to FASTElement #6760

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nicholasrice opened this issue Jun 9, 2023 · 0 comments
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area:fast-element Pertains to fast-element status:under-consideration Issue is being reviewed by the team.

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@nicholasrice
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nicholasrice commented Jun 9, 2023

💬 RFC

A feature I've been considering recently is the addition of a "connected" and "disconnected" lifecycle hook to FASTElement instances. These callbacks would be invoked by the ElementController just prior to exiting the connect() and disconnect() methods, respectively.

🔦 Context

Why would we want this? The browser already calls connectedCallback() and disconnectedCallback(), right? It does, but there-in lies the problem. In SSR scenarios, the defer-hydration attribute will prevent the ElementController from performing hydration work during the connectedCallback, including initializing template bindings, connecting behaviors, and re-binding observable values, only doing so after the defer-hydration attribute is removed. This means the element and ElementController's state within the connectedCallback could be very different between CSR and SSR+Hydration.

By introducing connected (and disconnected) and invoking the hooks from the ElementController, authors can craft components that operate under more consistent conditions between CSR and SSR + Hydration. Additionally, using these hooks and failing to call the super method would not break the ElementController.

💻 Examples

class MyElement extends FASTElement {
    connected() {
       // Always invoked after the ElementController has done connection work,
       // either during connectedCallback() in CSR scenarios or asynchronously
       // during defer-hydration scenarios.
    }
}
@nicholasrice nicholasrice added status:triage New Issue - needs triage area:fast-element Pertains to fast-element and removed status:triage New Issue - needs triage labels Jun 9, 2023
@janechu janechu added the status:under-consideration Issue is being reviewed by the team. label May 29, 2024
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Labels
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