read-frog (Agent Skills)

# AGENTS.md

## Testing Notes

- `src/utils/host/translate/api/__tests__/free-api.test.ts` depends on live external translation services.
- When running tests locally as an AI agent, set `SKIP_FREE_API=true`.
- If `SKIP_FREE_API=true` is set, treat `free-api.test.ts` as intentionally skipped during local validation.

## PR Notes

- PR titles must use conventional commit format, such as `fix(subtitles): ...`; avoid extra prefixes like `[codex]`.
- User-facing fixes and features should include a `.changeset/*.md` file for `@read-frog/extension` unless the change intentionally does not need a release. use conventional commit format for the changeset content.

---
title: Store Event Handlers in Refs
impact: LOW
impactDescription: stable subscriptions
tags: advanced, hooks, refs, event-handlers, optimization
---

## Store Event Handlers in Refs

Store callbacks in refs when used in effects that shouldn't re-subscribe on callback changes.

**Incorrect (re-subscribes on every render):**

```tsx
function useWindowEvent(event: string, handler: (e) => void) {
  useEffect(() => {
    window.addEventListener(event, handler)
    return () => window.removeEventListener(event, handler)
  }, [event, handler])
}
```

**Correct (stable subscription):**

```tsx
function useWindowEvent(event: string, handler: (e) => void) {
  const handlerRef = useRef(handler)
  useEffect(() => {
    handlerRef.current = handler
  }, [handler])

  useEffect(() => {
    const listener = (e) => handlerRef.current(e)
    window.addEventListener(event, listener)
    return () => window.removeEventListener(event, listener)
  }, [event])
}
```

**Alternative: use `useEffectEvent` if you're on latest React:**

```tsx
import { useEffectEvent } from 'react'

function useWindowEvent(event: string, handler: (e) => void) {
  const onEvent = useEffectEvent(handler)

  useEffect(() => {
    window.addEventListener(event, onEvent)
    return () => window.removeEventListener(event, onEvent)
  }, [event])
}
```

`useEffectEvent` provides a cleaner API for the same pattern: it creates a stable function reference that always calls the latest version of the handler.

---
title: Initialize App Once, Not Per Mount
impact: LOW-MEDIUM
impactDescription: avoids duplicate init in development
tags: initialization, useEffect, app-startup, side-effects
---

## Initialize App Once, Not Per Mount

Do not put app-wide initialization that must run once per app load inside `useEffect([])` of a component. Components can remount and effects will re-run. Use a module-level guard or top-level init in the entry module instead.

**Incorrect (runs twice in dev, re-runs on remount):**

```tsx
function Comp() {
  useEffect(() => {
    loadFromStorage()
    checkAuthToken()
  }, [])

  // ...
}
```

**Correct (once per app load):**

```tsx
let didInit = false

function Comp() {
  useEffect(() => {
    if (didInit) return
    didInit = true
    loadFromStorage()
    checkAuthToken()
  }, [])

  // ...
}
```

Reference: [Initializing the application](https://react.dev/learn/you-might-not-need-an-effect#initializing-the-application)