Preact Signals

@preact/signals updates a real Preact component when the frame signal changes. The component uses @vp-tw/likftc/preact to generate transition-safe keys.

Live before-and-after

Executed source

Imported verbatim with ?raw from every implementation file shown below. Playback timing and FLIP controls come from the shared demo harness.

main.tsxpreact-state-panels.tsx

src/preact-signals/main.tsxTSX · 25 linesCopy

/** @jsxImportSource preact */

import { useLikftc } from "@vp-tw/likftc/preact";
import { signal, type Signal } from "@preact/signals";
import { render } from "preact";

import { mountFrameworkDemo, type DemoFrameState, type DemoRuntime } from "../shared/demo.js";
import { PreactStatePanels } from "../shared/preact-state-panels.js";

function Runtime({ frameSignal }: { readonly frameSignal: Signal<DemoFrameState> }) {
  const frame = frameSignal.value;
  const entries = useLikftc(frame.items, { getId: (item) => item.id });
  return <PreactStatePanels entries={entries} frame={frame} />;
}

await mountFrameworkDemo("Preact Signals + Preact", (target, initialState): DemoRuntime => {
  const frameSignal = signal(initialState);
  render(<Runtime frameSignal={frameSignal} />, target);
  return {
    destroy: () => render(null, target),
    update: (frame) => {
      frameSignal.value = frame;
    },
  };
});

src/shared/preact-state-panels.tsxTSX · 64 linesCopy

/** @jsxImportSource preact */

import {
  createAfterRows,
  createBeforeRows,
  describeRow,
  type DemoFrameState,
  type DemoItem,
  type DemoRenderedRow,
} from "./demo.js";

function Row({ row }: { readonly row: DemoRenderedRow }) {
  return (
    <li
      class="runtime-row"
      data-collision={String(row.kind === "collision")}
      data-id={row.item.id}
      data-key={row.keyText}
      data-kind={row.kind}
      data-phase={row.kind === "exiting" ? "exiting" : "current"}
      data-slot={String(row.slot)}
    >
      <b>{row.item.id.toUpperCase()}</b>
      <span>{row.item.label}</span>
      <code>{row.keyText}</code>
      <em>{describeRow(row.kind)}</em>
    </li>
  );
}

function Panel({
  corrected,
  rows,
}: {
  readonly corrected: boolean;
  readonly rows: readonly DemoRenderedRow[];
}) {
  return (
    <article class="runtime-panel">
      <small>{corrected ? "WITH LIKFTC + PREACT SIGNALS" : "WITHOUT + PREACT SIGNALS"}</small>
      <h3>{corrected ? "Presence identity" : "Logical ID key"}</h3>
      <ol data-list={corrected ? "after" : "before"}>
        {rows.map((row) => (
          <Row key={row.key} row={row} />
        ))}
      </ol>
    </article>
  );
}

export function PreactStatePanels({
  entries,
  frame,
}: {
  readonly entries: readonly { readonly item: DemoItem; readonly key: number }[];
  readonly frame: DemoFrameState;
}) {
  return (
    <div class="runtime-grid">
      <Panel corrected={false} rows={createBeforeRows(frame)} />
      <Panel corrected rows={createAfterRows(frame, entries)} />
    </div>
  );
}

The default TSX tab shows the signal read and useLikftc() call together.