What are the differences between MobX and Redux, and how to choose?

MobX and Redux are both popular state management libraries, but they have significant differences in design philosophy and usage. Choosing between them depends on project requirements, team preferences, and specific scenarios.

Core Design Philosophy

MobX

• Observer pattern based: Automatically tracks state changes without manual subscription
• Imperative programming: Directly modify state, more intuitive
• Transparent reactivity: State changes automatically trigger updates
• High flexibility: Does not enforce specific code structure

Redux

• Functional programming based: Uses pure functions to handle state changes
• Declarative programming: Modify state by dispatching actions
• Unidirectional data flow: Action → Reducer → Store → View
• High standardization: Enforces specific code structure

Code Comparison

MobX Example

javascript
import { observable, action, computed, makeAutoObservable } from 'mobx';

class TodoStore {
  todos = [];
  filter = 'all';
  
  constructor() {
    makeAutoObservable(this);
  }
  
  @computed get filteredTodos() {
    switch (this.filter) {
      case 'completed':
        return this.todos.filter(todo => todo.completed);
      case 'active':
        return this.todos.filter(todo => !todo.completed);
      default:
        return this.todos;
    }
  }
  
  @action addTodo(text) {
    this.todos.push({ id: Date.now(), text, completed: false });
  }
  
  @action toggleTodo(id) {
    const todo = this.todos.find(t => t.id === id);
    if (todo) todo.completed = !todo.completed;
  }
  
  @action setFilter(filter) {
    this.filter = filter;
  }
}

const store = new TodoStore();

// Usage
store.addTodo('Learn MobX');
store.toggleTodo(store.todos[0].id);

Redux Example

javascript
import { createStore } from 'redux';

// Action Types
const ADD_TODO = 'ADD_TODO';
const TOGGLE_TODO = 'TOGGLE_TODO';
const SET_FILTER = 'SET_FILTER';

// Action Creators
const addTodo = (text) => ({ type: ADD_TODO, payload: { id: Date.now(), text, completed: false } });
const toggleTodo = (id) => ({ type: TOGGLE_TODO, payload: id });
const setFilter = (filter) => ({ type: SET_FILTER, payload: filter });

// Reducer
const initialState = {
  todos: [],
  filter: 'all'
};

function todoReducer(state = initialState, action) {
  switch (action.type) {
    case ADD_TODO:
      return { ...state, todos: [...state.todos, action.payload] };
    case TOGGLE_TODO:
      return {
        ...state,
        todos: state.todos.map(todo =>
          todo.id === action.payload ? { ...todo, completed: !todo.completed } : todo
        )
      };
    case SET_FILTER:
      return { ...state, filter: action.payload };
    default:
      return state;
  }
}

const store = createStore(todoReducer);

// Selector
const selectFilteredTodos = (state) => {
  switch (state.filter) {
    case 'completed':
      return state.todos.filter(todo => todo.completed);
    case 'active':
      return state.todos.filter(todo => !todo.completed);
    default:
      return state.todos;
  }
};

// Usage
store.dispatch(addTodo('Learn Redux'));
store.dispatch(toggleTodo(store.getState().todos[0].id));

Detailed Comparison

Feature	MobX	Redux
Programming paradigm	Imperative, OOP	Functional, declarative
State tracking	Automatic tracking	Manual subscription
State modification	Direct modification	Through action
Code volume	Less	More
Learning curve	Gentler	Steeper
Flexibility	High	Low
Standardization	Low	High
Debugging tools	MobX DevTools	Redux DevTools
Time travel	Limited support	Full support
Middleware	Not needed	Rich (redux-thunk, redux-saga, etc.)
Performance	Automatic optimization	Requires manual optimization
State structure	Can be nested	Recommend flattening
Type support	Good	Requires additional configuration

Use Cases

Scenarios suitable for MobX

1. Rapid development: Need rapid prototyping or small projects
2. Complex state structure: Complex and nested state structure
3. Team experience: Team more familiar with OOP
4. Flexibility first: Need more code flexibility
5. Learning cost: Want to reduce learning cost

javascript
// MobX suitable for complex nested state
class UserStore {
  @observable user = {
    profile: {
      name: '',
      email: '',
      address: {
        city: '',
        country: ''
      }
    },
    preferences: {
      theme: 'light',
      language: 'en'
    }
  };
  
  @action updateCity(city) {
    this.user.profile.address.city = city; // Directly modify nested properties
  }
}

Scenarios suitable for Redux

1. Large projects: Large projects requiring strict standards
2. Team collaboration: Multi-person collaboration, need unified code standards
3. Time travel: Need complete time travel debugging
4. Middleware needs: Need rich middleware ecosystem
5. Functional programming: Team prefers functional programming paradigm

javascript
// Redux suitable for flattened state
const initialState = {
  users: {
    byId: {},
    allIds: []
  },
  profiles: {
    byId: {},
    allIds: []
  },
  addresses: {
    byId: {},
    allIds: []
  }
};

// Handle state changes through reducers
function reducer(state = initialState, action) {
  switch (action.type) {
    case UPDATE_CITY:
      return {
        ...state,
        addresses: {
          ...state.addresses,
          byId: {
            ...state.addresses.byId,
            [action.payload.id]: {
              ...state.addresses.byId[action.payload.id],
              city: action.payload.city
            }
          }
        }
      };
    default:
      return state;
  }
}

Performance Comparison

MobX Performance Advantages

1. Automatic optimization: Automatically tracks dependencies, only updates necessary components
2. Batch updates: State changes within actions are batched
3. Lazy evaluation: Computed values only calculated when accessed

javascript
// MobX automatic optimization
class Store {
  @observable items = [];
  
  @computed get expensiveValue() {
    console.log('Computing expensive value');
    return this.items.reduce((sum, item) => sum + item.value, 0);
  }
}

// Only calculated when accessing expensiveValue
console.log(store.expensiveValue); // Calculate once
console.log(store.expensiveValue); // Use cache, no calculation

Redux Performance Challenges

1. Manual optimization: Need to use reselect, memo and other tools to optimize
2. Full comparison: Every dispatch compares the entire state tree
3. Manual subscription: Need to manually select needed data

javascript
// Redux requires manual optimization
import { createSelector } from 'reselect';

const selectItems = (state) => state.items;
const selectExpensiveValue = createSelector(
  [selectItems],
  (items) => {
    console.log('Computing expensive value');
    return items.reduce((sum, item) => sum + item.value, 0);
  }
);

// Need to manually select data
const value = selectExpensiveValue(store.getState());

Debugging Comparison

MobX Debugging

javascript
// Use MobX DevTools
import { makeObservable, observable, action } from 'mobx';

class Store {
  @observable count = 0;
  
  constructor() {
    makeObservable(this);
  }
  
  @action increment() {
    this.count++;
  }
}

// View state changes in browser

Redux Debugging

javascript
// Use Redux DevTools
import { createStore } from 'redux';

const store = createStore(
  reducer,
  window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__()
);

// Can view complete action history, state changes, and time travel

Migration Suggestions

Migrating from MobX to Redux

1. Refactor state structure: Flatten nested state
2. Create action types: Define all possible actions
3. Write reducers: Move state modification logic to reducers
4. Use middleware: Add middleware as needed
5. Update components: Use useSelector and useDispatch

Migrating from Redux to MobX

1. Create stores: Convert reducer logic to stores
2. Use observable: Convert state to observable
3. Add actions: Convert action creators to actions
4. Update components: Use observer or useObserver
5. Simplify code: Remove unnecessary boilerplate

Summary

Choose MobX if:

• Need rapid development
• State structure is complex and nested
• Team more familiar with OOP
• Want to reduce learning cost
• Need more code flexibility

Choose Redux if:

• Project scale is large
• Need strict code standards
• Need complete time travel debugging
• Need rich middleware ecosystem
• Team prefers functional programming

Both are excellent state management libraries, and the choice should be based on project requirements and team situation. In actual projects, you can also mix and match based on the characteristics of different modules.