# `react-doctor/no-promise-then-side-effect-in-effect-without-catch`

Effect promise .then sets state with no catch

- **Category:** Bugs
- **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-promise-then-side-effect-in-effect-without-catch`. 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
const C = ({ urls }) => {
  const [, setValue] = useState();
  useEffect(() => {
    let request;
    for (const url of urls) {
      request = fetch(url).then((value) => setValue(value));
    }
    request.catch(() => setValue(null));
  }, [urls]);
};
```

### Corrected pattern

```ts
const C = ({ urls }) => {
  const [, setValue] = useState();
  useEffect(() => {
    let isCurrent = true;
    for (const url of urls) {
      void fetch(url)
        .then((value) => {
          if (isCurrent) setValue(value);
        })
        .catch(() => {
          if (isCurrent) setValue(null);
        });
    }
    return () => {
      isCurrent = false;
    };
  }, [urls]);
};
```

## 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-promise-then-side-effect-in-effect-without-catch` diagnostic in the current repository.

Required change:
- Handle rejections from effect promises. Clear loading state in `finally`, and ignore stale results after cleanup.

Reference transformation:

Before:
```ts
const C = ({ urls }) => {
  const [, setValue] = useState();
  useEffect(() => {
    let request;
    for (const url of urls) {
      request = fetch(url).then((value) => setValue(value));
    }
    request.catch(() => setValue(null));
  }, [urls]);
};
```

After:
```ts
const C = ({ urls }) => {
  const [, setValue] = useState();
  useEffect(() => {
    let isCurrent = true;
    for (const url of urls) {
      void fetch(url)
        .then((value) => {
          if (isCurrent) setValue(value);
        })
        .catch(() => {
          if (isCurrent) setValue(null);
        });
    }
    return () => {
      isCurrent = false;
    };
  }, [urls]);
};
```

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.
- 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.
````