When using an immer producer function, which is a function that creates a draft state and allows us to make modifications to it, we have two options for how we handle the state updates: returning a new value or modifying the draft itself. Let’s understand each option in detail with examples.
Option 1: Returning a New Value
In this approach, the immer producer function should return a new value that represents the updated state. This is useful when you want to completely replace the existing state with a new one rather than modifying it directly. Here’s an example:
const state = {
count: 0,
};
const newState = produce(state, (draft) => {
draft.count += 1;
});
console.log(newState.count); // Output: 1
In the above example, we start with an initial state object that has a “count” property with a value of 0. Inside the immer producer function, we modify the “count” property of the draft by incrementing it by 1. The “produce” function then returns a new state object with the updated “count” value, which is assigned to the “newState” variable. Finally, we can access the updated state by accessing the “count” property of the “newState” object.
Option 2: Modifying the Draft
In this approach, the immer producer function directly modifies the draft state without returning a new value. This is useful when you want to make in-place mutations to the draft object. Here’s an example:
const state = {
count: 0,
};
produce(state, (draft) => {
draft.count += 1;
});
console.log(state.count); // Output: 1
In the above example, we have the same initial state object with a “count” property. Inside the immer producer function, we modify the “count” property of the draft directly. Since we are not returning a new value, the “state” object itself is modified. Therefore, when we access the “count” property of the “state” object outside the producer, we can see the updated value directly.
It’s important to note that both options achieve the same result, but the approach you choose depends on the desired outcome and your application’s requirements. Returning a new value ensures immutability and can be useful for tracking state changes, while modifying the draft directly can provide performance benefits when dealing with large state objects.