How to correctly change the state of redux, react-redux?

Question

React

Hello.

I started to study redux, but I didn’t understand how to change the state (store) correctly, I

read several articles everywhere they say you need to use pure functions.
I know what pure functions are, but I still don’t understand how to change the state.

Now I do this

function reducer(state, action){

  switch (action.type) {

    case 'LOGGED': {

      return {
        isLogged : true,
        user: action.user 
      }

    };

    default: return state;

  }

}

export default reducer;

Correct or not?

Answer 1

Just stick to data immutability:

return {
    ...state,          // Разворачиваем старое состояние
    isLogged : true,   // обновляем свойства которые нужно
    user: action.user  // обновляем свойства которые нужно
}

Immutability:

Immutable is an object whose state cannot be changed after creation. Any modification of such an object will always result in a new object, while the old object will not change.

Answer 2

change state + pure functions = a function that does not change the old state, but calculates and returns a new state based on the old one (and, in particular, also based on the received action)