Hacktoberfest 2026: as issues que os mantenedores marcaram para outubro, abertas e boas para iniciantes. Ver issues do Hacktoberfest

[feat]: slotController synchronous `hostUpdated()`

Aberta
  • Algo errado?
#3,103 0 comentários 0 reações 0 responsáveis Ver no GitHub

Ninguém assumiu esta issue ainda.

Avaliação

Dificuldade
4/5
Tempo estimado
3-5 dias
Facilidade para iniciantes
55/100
Tipo de issue
Funcionalidade
Clareza
Razoavelmente clara
Status de atividade
Pouca atividade
Stack de tecnologia
typescript
Domínio
frontend

Direção de pesquisa

Start by locating the slotController implementation and the SlotControllerPublicAPI declaration, then trace hostConnected, #initSlotMap, the MutationObserver, and the hasSlotted(), isEmpty(), and getSlotted() methods. Implement the synchronous lifecycle described in the issue and verify initial connection, reconnection, and child mutations produce correct slot state without an async timing gap.

Escrita pelo modelo de indexação a partir do texto da issue.

Descrição

Alternative approach:

synchronous hostUpdated() instead of async fallback

The current fix adds a fallback in getSlotted() to query slot elements directly when #slotRecords hasn't been populated yet. This addresses the symptom but leaves the root cause: hostConnected and #initSlotMap are async, creating a timing gap where no data source exists.

The gap also affects hasSlotted() and isEmpty(), which aren't addressed here.

Why hostConnected is async

Both hostConnected and #initSlotMap await host.updateComplete just to ensure the shadow DOM exists so they can query for elements. But Lit already provides a synchronous hook that guarantees this: hostUpdated(), which runs after every render when the DOM has been committed.

Suggested change

Make hostConnected synchronous (just sets up the MutationObserver), move record initialization to hostUpdated(), and have the MutationObserver trigger a re-render instead of calling #initSlotMap directly:

  hostConnected(): void {
    this.#mo.observe(this.host, { childList: true });
    this.#slotRecords.clear();
  }

  hostUpdated(): void {
    if (this.#slotRecords.size === 0) {
      for (let slotName of this.#slotNames.concat(Object.values(this.#deprecations))) {
        slotName ||= SlotController.default;
        const slot = this.#getSlotElement(slotName);
        if (slot) {
          this.#slotRecords.set(slotName, new SlotRecord(slot, slotName, this.host));
        }
      }
      if (this.#slotRecords.size > 0) {
        this.host.requestUpdate();
      }
    }
  }

The MutationObserver callback becomes:

#mo = new MutationObserver(() => this.host.requestUpdate());

And #initSlotMap can be removed entirely.

This also requires updating the SlotControllerPublicAPI declaration to match:

hostConnected?(): void;

Why this works

  • First render: Records empty, isEmpty() returns true (matches SSR server behavior). hostUpdated() populates records and calls requestUpdate().
  • Second render: Records exist, isEmpty()/getSlotted() read live DOM via SlotRecord getters, correct results. hostUpdated() sees records exist, no requestUpdate(), no infinite loop.
  • MutationObserver: Child changes trigger requestUpdate() → re-render → SlotRecord getters reflect new DOM state. No record rebuild needed since they query live DOM.
  • Reconnection: hostConnected clears records → next render → hostUpdated() repopulates.

What this fixes that the current PR doesn't

  • hasSlotted() and isEmpty() have the same timing gap, they also read from #slotRecords and return incorrect results before async init completes. The hostUpdated() approach fixes all three methods.
  • Eliminates the async architecture that caused the issue rather than working around it.

Trade-off

The two-render pattern on initial connection is inherent <slot> elements are created by render(), so the first render can't know about them. This was already the case with the async approach.

We can spin this off to another issue if we feel the need

Originally posted by @zeroedin in https://github.com/patternfly/patternfly-elements/issues/3093#issuecomment-4252752632

Linguagem predominante
TypeScript
Estrelas
395
Forks
107
Nenhum PR com merge em 30d

Preparar o ambiente

Primeiros passos

  1. Leia a issue inteira e depois o guia de contribuição do projeto.
  2. Comente na issue dizendo que vai assumir — evita que duas pessoas façam o mesmo trabalho.
  3. Faça um fork do repositório e trabalhe em uma branch.
  4. Abra um pull request que referencie o número da issue.

Mais de patternfly/patternfly-elements

Todas as issues de patternfly/patternfly-elements

Issues semelhantes

Mais issues de TypeScript

Receba novas issues na sua caixa de entrada

Um resumo curto de issues do GitHub para quem está começando.