## Issues with useEffect dependency array

React use [shallow comparision](https://learntechsystems.com/what-is-shallow-comparison-in-js/) (values are equals in case of primitive types. In case of object it just check the reference) to check if the dependency changes between renders, this can conduce to bugs in the following situa

### Always use a depency array

```js
useEffect(() => {
  setCount((count) => count + 1);
}, []);
```

### Function as dependency

React re defines functions on every render, so the dependency always changes, use `useCallback` to memoize the function so it doesn't change

```js
const logResult = useCallback(() => {
  return 2 + 2;
}, []);

useEffect(()=> {
  setCount((count) => count + 1);
}, [logResult]);
```

### Array as dependency

The reference to an array changes in every render, use `useRef` so it doesn't change

```js
const [count, setCount] = useState(0);
//extract the 'current' property and assign it a value
const { current: myArray } = useRef(["one", "two", "three"]);

useEffect(() => {
  setCount((count) => count + 1);
}, [myArray]);
```
### Object as dependency

The reference to an object changes in every render, use `useMemo` so it doesn't change

```js
const person = useMemo(
  () => ({ name: "Rue", age: 17 }),
  [] //no dependencies so the value doesn't change
);
useEffect(() => {
  setCount((count) => count + 1);
}, [person]);
```

[source](https://blog.logrocket.com/solve-react-useeffect-hook-infinite-loop-patterns/)


## Reset a component state

React utiliza la propiedad `key` para poder identificar un componente, esta propiedad puede ser omitida y react le asignará una en base a su posición en el Virtual DOM Tree.

Cuando la propiedad cambia, React entiende que el componente no es el mismo, por lo que destruye el componente actual y crea uno nuevo, lo que por ende, tiene el estado inicial.

Para esto tenemos dos opciones:
- Pasar alguna propiedad de los datos como key.
- Generar un valor único localmente.

Lo primero es como pasar el ID de un usuario. para lo segundo podemos usar lo siguiente:

```jsx
import { useRef } from 'react';

export default function Parent() {
  const key = useRef(crypto.randomUUID());

	const resetComponent = () => key.current = crypto.randomUUID();

  return (
		<div>
			<Component key={key.current} />
			<button onClick={() => resetComponent()}></button>
		</div>
  )
}
```
