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`createRoot`'s dispose function keeps `fn` alive, so `<For>`/`<Index>` rows retain removed list items

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#4,095 0 comentarios 0 reacciones 0 asignados Ver en GitHub

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@boombang ya está trabajando en esto.

Desde el 15/10/2026.

  • #4096 de @boombang — abierto

Evaluación

Dificultad
4/5
Tiempo estimado
1-2 días
Aptitud para principiantes
45/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
javascript, typescript
Área
frontend, performance

Línea de trabajo

Start with createRoot and the updateFn line that builds the dispose closure, then trace how mapArray and indexArray store each row's disposer in disposers. Run the repro script with node --expose-gc --conditions=browser repro.mjs. Done means both lines print false, and the existing tests for createRoot and the array helpers still pass.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

1.x
Describe the bug

createRoot creates the dispose function it passes to fn inside its own scope:

updateFn = unowned ? ... : () => fn(() => untrack(() => cleanNode(root)));

That scope also holds fn, because updateFn closes over it. So anything that keeps the dispose function also keeps fn, and everything fn closes over.

mapArray and indexArray keep every row's dispose function in disposers. Every row's fn is mapper, and mapper closes over newItems, the list that was current when the row was created. So a mounted row keeps that whole list reachable, including items that were removed from the list later.

We found this in production. A long-lived <For> row kept a list it was created from, and with it a replaced document of a few hundred MB.

Your Example Website or App

Standalone script below (Node 22, solid-js 1.9.17, client build).

Steps to Reproduce the Bug or Issue
// npm i [email protected]
// node --expose-gc --conditions=browser repro.mjs
import { createRoot, createSignal, createMemo, mapArray, indexArray } from "solid-js";

const collect = async () => {
  // WeakRef targets stay alive until the current job ends.
  await new Promise(r => setTimeout(r, 0));
  globalThis.gc();
};

// A row created from [kept, removed] stays mounted after the list becomes [kept].
async function check(name, map) {
  const kept = { name: "kept" };
  let removed, setList;
  const dispose = createRoot(dispose => {
    const [list, set] = createSignal(
      (() => {
        const item = { name: "removed" };
        removed = new WeakRef(item);
        return [kept, item];
      })()
    );
    setList = set;
    createMemo(map(list))();
    return dispose;
  });
  setList([kept]);
  await collect();
  console.log(`${name}: removed item still reachable:`, removed.deref() !== undefined);
  dispose();
}

await check("mapArray (<For>)", list => mapArray(list, item => item.name));
await check("indexArray (<Index>)", list => indexArray(list, item => item().name));

Output:

mapArray (<For>): removed item still reachable: true
indexArray (<Index>): removed item still reachable: true

The dev build (dist/dev.js) gives the same output, and so does Bun (JavaScriptCore) with Bun.gc(true).

Expected behavior

Once the row for removed is disposed, nothing should keep removed reachable, so both lines should print false. They do once the dispose function is created outside createRoot's scope, in both V8 and JavaScriptCore.

Platform
  • solid-js: 1.9.17 (main)
  • Node 22.23 (V8), Bun 1.4.2 (JavaScriptCore)
Additional context

I haven't checked next (2.0) yet. The fix for 1.x is in the PR linked below.

Lenguaje dominante
TypeScript
Estrellas
36.1k
Forks
1.1k
Merge medio
11 h 37 min
PR fusionados (30 d)
344

Preparar el entorno

Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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