I'm just starting with programming and have recently written my first app in React, and while it does work, I'm not sure if I'm handling my internal state correctly. My question is whether the setState method creates an immutable deep copy of the "prevState" or not necessarily? To show an example: 

```
 menuAddRecHandler = () => {
    this.setState((prevState) => {
      const updatedState = {...prevState};
      const dayInd = updatedState.menu.recipes.findIndex(item => item.dayNum === updatedState.menuInternal.currentDay);
      updatedState.menu.recipes[dayInd].recList.push({
        name: prevState.menuInternal.menuRecSelect,
        portions: prevState.menuInternal.menuNumPortInput
      });
      return updatedState;
    })
  }

```

In my handler I am pushing an object to a nested array of the updatedState object which was copied over from prevState by the spread operator. Now I know that the spread operator makes only a shallow copy, but is the prevState supplied internally by the setState method also shallow, and does that mean that I am actually mutating my state directly by invoking this handler? If so, how do I fix this issue? Thank you.