# `react-doctor/no-unthrottled-scroll-mutation`

Scroll handler drives animation every event

- **Category:** Performance
- **Severity:** warn
- **Source:** oxlint-plugin-react-doctor
- **Framework:** global
- **Enabled when:** react

## Validate the diagnostic

Confirm the reported code matches this rule before you edit it.

Confirm the reported code matches `react-doctor/no-unthrottled-scroll-mutation`. Compare it with the Before example and verify the same API, framework, and execution context. Treat it as a false positive only when one of those conditions differs.

## Compare the code

The corrected pattern shows a focused way to address the diagnostic.

### Reported pattern

```ts
import { useEffect } from "react";

const Hero = () => {
  useEffect(() => {
    const hero = document.querySelector(".hero");
    if (!hero) return;
    const onScroll = () => {
      hero.style.transform = `translateY(${window.scrollY}px)`;
    };
    window.addEventListener("scroll", onScroll);
    return () => window.removeEventListener("scroll", onScroll);
  }, []);
  return null;
};
```

### Corrected pattern

```ts
import { useEffect } from "react";

const Hero = () => {
  useEffect(() => {
    const hero = document.querySelector(".hero");
    if (!hero) return;
    let timerId: number | undefined;
    const onScroll = () => {
      if (timerId) return;
      timerId = window.setTimeout(() => {
        hero.style.transform = `translateY(${window.scrollY}px)`;
        timerId = undefined;
      }, 100);
    };
    window.addEventListener("scroll", onScroll);
    return () => {
      window.clearTimeout(timerId);
      window.removeEventListener("scroll", onScroll);
    };
  }, []);
  return null;
};
```

## How to fix

Use the corrected pattern as a reference. Preserve behavior that the rule does not require you to change.

### Copyable fix prompt

Copy this self-contained prompt into your coding agent after you confirm the diagnostic.

````text
Fix every confirmed `react-doctor/no-unthrottled-scroll-mutation` diagnostic in the current repository.

Required change:
- Use a scroll or view timeline, IntersectionObserver, or a real timer throttle so animation work does not run for every scroll event.

Reference transformation:

Before:
```ts
import { useEffect } from "react";

const Hero = () => {
  useEffect(() => {
    const hero = document.querySelector(".hero");
    if (!hero) return;
    const onScroll = () => {
      hero.style.transform = `translateY(${window.scrollY}px)`;
    };
    window.addEventListener("scroll", onScroll);
    return () => window.removeEventListener("scroll", onScroll);
  }, []);
  return null;
};
```

After:
```ts
import { useEffect } from "react";

const Hero = () => {
  useEffect(() => {
    const hero = document.querySelector(".hero");
    if (!hero) return;
    let timerId: number | undefined;
    const onScroll = () => {
      if (timerId) return;
      timerId = window.setTimeout(() => {
        hero.style.transform = `translateY(${window.scrollY}px)`;
        timerId = undefined;
      }, 100);
    };
    window.addEventListener("scroll", onScroll);
    return () => {
      window.clearTimeout(timerId);
      window.removeEventListener("scroll", onScroll);
    };
  }, []);
  return null;
};
```

Constraints:
- Confirm the reported code matches the Before pattern.
- Make the smallest change that fixes the root cause.
- Preserve behavior and interfaces unrelated to this diagnostic.
- Reuse existing project components, utilities, and conventions.
- Do not introduce render-phase side effects, render-phase state updates, or Hooks rule violations.
- Preserve resource ownership and cleanup. Do not move work into a hotter render or frame path.
- Adapt identifiers and framework details instead of copying blindly.
- Do not disable the rule or suppress matching code.
- Confirm this rule is enabled for the project: `react`.

Verification:
- Run focused tests for the changed behavior.
- Run React Doctor and confirm this diagnostic no longer appears.
- Report the files changed and any checks you could not run.
````