react-hooks/void-use-memo

useMemo() caches what its callback returns. A callback that returns nothing caches undefined, which usually means a forgotten return, or a side effect that belongs in useEffect(). React can skip or repeat the callback, so a side effect in it won't run when you expect.

The rule also reports a useMemo() call if its result is never used.

Configure#

Off by default. To turn it on:

bunfig.toml

[lint.rules]
"react-hooks/void-use-memo" = "error" # or "warn"

Examples#

Reported:

import { useMemo } from "react";

function Report({ rows }) {
  const visible = useMemo(() => {
    rows.filter(row => !row.hidden);
  }, [rows]);
  return <Table rows={visible} />;
}

import { useMemo } from "react";

function Report({ rows }) {
  useMemo(() => rows.filter(row => !row.hidden), [rows]);
  return <Table rows={rows} />;
}

Not reported:

import { useMemo } from "react";

function Report({ rows }) {
  const visible = useMemo(() => {
    return rows.filter(row => !row.hidden);
  }, [rows]);
  return <Table rows={visible} />;
}

Side effects go in an effect:

import { useEffect } from "react";

function Report({ rows }) {
  useEffect(() => {
    track("report", rows.length);
  }, [rows]);
  return <Table rows={rows} />;
}