Implementing a Custom Redux with Immer-Like Functionality in JavaScript

Redux is a popular state management library for JavaScript applications, and Immer is a powerful utility that helps manage immutable state in a more intuitive way. Immer allows you to write "mutable" code that produces immutable state updates, making it easier to manage complex state transformations.

we'll implement a custom version of Redux that utilizes Immer-like functionality to manage immutable state.

What is Immer?

Immer simplifies working with immutable state by allowing you to modify a "draft" version of your state, which Immer then uses to produce a new, immutable state. This approach is particularly useful in Redux, where immutability is a key principle.

Real Interview Insights

Interviewers might ask you to:

  • Implement a Redux-like state management system that utilizes an Immer-like approach to state updates.
  • Ensure that the state updates remain immutable while allowing developers to write code that appears mutable.
  • Handle common Redux patterns like actions, reducers, and middleware.

Implementing Custom Redux with Immer-Like Functionality

Here’s how you can implement a custom Redux with Immer-like functionality:

  1. Create a produce function: This function will handle the state drafting and production of the final immutable state.

  2. Implement a custom Redux store: This will include dispatching actions, updating state, and subscribing to changes.

Step 1: Implementing the produce Function

The produce function will take an initial state and a recipe function (which "mutates" the draft) and will return the new state.

function produce(baseState, producer) {
  const draftState = JSON.parse(JSON.stringify(baseState)); // Create a deep copy of the base state
 
  producer(draftState); // Allow mutation of the draft state
 
  return draftState; // Return the mutated draft state as the new immutable state
}

Step 2: Implementing the Custom Redux Store

We’ll now create a simple Redux-like store that utilizes the produce function for state updates.

function createStore(reducer) {
  let state;
  let listeners = [];
 
  const getState = () => state;
 
  const dispatch = (action) => {
    state = produce(state, (draft) => reducer(draft, action));
    listeners.forEach(listener => listener());
  };
 
  const subscribe = (listener) => {
    listeners.push(listener);
    return () => {
      listeners = listeners.filter(l => l !== listener);
    };
  };
 
  // Initialize the store with an undefined action to set the initial state
  dispatch({ type: '@@INIT' });
 
  return { getState, dispatch, subscribe };
}

Example Usage

Let’s see how you can use this custom Redux store with Immer-like functionality:

// Define the initial state and a reducer function
const initialState = {
  todos: []
};
 
function todoReducer(state = initialState, action) {
  switch (action.type) {
    case 'ADD_TODO':
      state.todos.push({ text: action.text, completed: false });
      break;
    case 'TOGGLE_TODO':
      const todo = state.todos[action.index];
      todo.completed = !todo.completed;
      break;
    default:
      return state;
  }
}
 
// Create the store
const store = createStore(todoReducer);
 
// Subscribe to state changes
store.subscribe(() => console.log(store.getState()));
 
// Dispatch some actions
store.dispatch({ type: 'ADD_TODO', text: 'Learn Redux' });
store.dispatch({ type: 'ADD_TODO', text: 'Implement custom Redux with Immer' });
store.dispatch({ type: 'TOGGLE_TODO', index: 0 });

Explanation:

  • produce Function: This function allows you to write state updates as if you were mutating the state directly. It creates a deep copy of the state, applies the mutations, and then returns the new immutable state.
  • Custom Redux Store: The store manages the state, allows dispatching actions, and subscribes to state changes. It uses the produce function to ensure that state updates are handled immutably.

Handling Edge Cases

  1. Nested State: The produce function creates a deep copy, so nested objects are correctly handled and remain immutable.
  2. Action Types: Your reducer should handle various action types and default cases to ensure robust state management.
  3. Middleware Support: While not implemented here, you can extend this custom Redux store to support middleware for handling async actions, logging, etc.

Use Cases for Immer in Redux

  1. Simplified State Updates: Immer allows for more readable and maintainable code by letting you write updates as if the state were mutable.
  2. Complex State Management: For applications with deeply nested state, Immer simplifies the process of updating specific parts of the state.
  3. Ensuring Immutability: By using Immer, you can ensure that your state remains immutable without having to write complex immutability logic.