Global Libraries - MSDN Documentation

Global Libraries for State Management

Global libraries provide robust solutions for managing application state across different components, especially in large and complex applications. They offer patterns and tools to make state predictable and easier to debug.

Overview

When your application's state grows beyond what local state or the Context API can efficiently handle, global state management libraries become invaluable. These libraries typically centralize your application's state in a single location, often referred to as a "store," and provide mechanisms for components to access and modify this state.

Key Concepts

Store: A central repository for your application's entire state.
Actions/Mutations: Functions or objects that describe intended state changes.
Reducers/Getters: Functions that handle state updates based on actions and retrieve state values.
Dispatch/Commit: Mechanisms used by components to send actions to the store.
Subscribe/Connect: Methods components use to receive state updates from the store.

Popular Global Libraries

1. Redux

Redux is a predictable state container for JavaScript applications. It's known for its strict unidirectional data flow, making state changes traceable and easier to debug.

Core Principles:

Single source of truth: The state of your whole application is stored in an object tree within a single store.
State is read-only: The only way to change the state is to emit an action, an object describing what happened.
Changes are made with pure functions: To specify how the state tree is transformed by actions, you write pure reducers.

Basic Example:


// actions.js
export const increment = () => ({ type: 'INCREMENT' });
export const decrement = () => ({ type: 'DECREMENT' });

// reducers.js
const initialState = { count: 0 };

function counterReducer(state = initialState, action) {
    switch (action.type) {
        case 'INCREMENT':
            return { ...state, count: state.count + 1 };
        case 'DECREMENT':
            return { ...state, count: state.count - 1 };
        default:
            return state;
    }
}
export default counterReducer;

// store.js
import { createStore } from 'redux';
import counterReducer from './reducers';

const store = createStore(counterReducer);
export default store;

// App.js (React example)
import React from 'react';
import { useSelector, useDispatch } from 'react-redux';
import { increment, decrement } from './actions';

function Counter() {
    const count = useSelector(state => state.count);
    const dispatch = useDispatch();

    return (
        
            Count: {count}
            
            
        
    );
}

Resources: Redux Official Website

2. MobX

MobX makes state management simple and scalable by transparently applying functional reactive programming (FRP) to your codebase. It allows you to manage your application's state by using plain JavaScript objects and letting MobX handle the rest.

Key Features:

Observable state: MobX tracks changes to observable data.
Computed values: Values derived from observable state that automatically update.
Actions: Functions that modify observable state.

Basic Example:


import { makeObservable, observable, computed, action } from "mobx";

class CounterStore {
    count = 0;

    constructor() {
        makeObservable(this, {
            count: observable,
            doubleCount: computed,
            increment: action,
            decrement: action
        });
    }

    get doubleCount() {
        return this.count * 2;
    }

    increment() {
        this.count++;
    }

    decrement() {
        this.count--;
    }
}

const counterStore = new CounterStore();
export default counterStore;

// App.js (React example using mobx-react-lite)
import React from 'react';
import { observer } from "mobx-react-lite";
import counterStore from './CounterStore';

const Counter = observer(() => {
    return (
        
            Count: {counterStore.count}
            Double Count: {counterStore.doubleCount}
            
            
        
    );
});
export default Counter;

Resources: MobX Official Website

When to use Global Libraries?

Consider using a global state management library when:

State needs to be accessed by many components at different levels of the component tree.
State updates are frequent and complex.
You need a centralized and predictable way to manage application state.
Your application is growing in complexity and size.

Choosing the Right Library

The choice between libraries like Redux and MobX often depends on project requirements, team familiarity, and desired level of boilerplate. Redux offers strong predictability and a rich ecosystem, while MobX prioritizes simplicity and less boilerplate.