So, today I revisited my 5 months old code and was like "What? Did I really wrote this horrible code?" 😐️ 🙂️ 😃️🔫️

```js
setState((initVal) => {
initVal.food = 'burger';
return initVal;
});
```

The function above change its argument's value, which is terrible thing to do, since it will also change the original value passed to the function. A variable's value for example. Making it an impure function.