工程化与框架系列（10）--微前端架构

微前端架构 🏗️

微前端是一种将前端应用分解成更小、更易管理的独立部分的架构模式。本文将详细介绍微前端的核心概念、实现方案和最佳实践。

微前端概述 🌟

💡 小知识：微前端的核心理念是将前端应用分解成一系列独立部署、松耦合的小型应用，每个应用可以由不同的团队使用不同的技术栈开发。

为什么需要微前端

在大型前端应用开发中，微前端架构能带来以下优势：

技术栈灵活性
- 支持多框架共存
- 渐进式技术迁移
- 团队技术选择自由
- 复用已有应用资产
团队自主性
- 独立开发部署
- 团队边界清晰
- 降低协作成本
- 提高开发效率
应用可维护性
- 代码库规模可控
- 模块职责单一
- 降低耦合度
- 简化测试和部署
性能优化空间
- 按需加载应用
- 独立缓存策略
- 资源并行加载
- 性能瓶颈隔离

实现方案详解 ⚡

基于路由的实现

// router-based.ts
interface MicroApp {
    name: string;
    entry: string;
    container: string;
    activeRule: string;
}

export class RouterBasedMicroFrontend {
    private apps: MicroApp[] = [];

    constructor(apps: MicroApp[]) {
        this.apps = apps;
        this.initializeRouter();
    }

    private initializeRouter(): void {
        window.addEventListener('popstate', () => {
            this.handleRouteChange();
        });

        // 初始化时加载匹配的应用
        this.handleRouteChange();
    }

    private handleRouteChange(): void {
        const path = window.location.pathname;
        const app = this.apps.find(app => 
            path.startsWith(app.activeRule)
        );

        if (app) {
            this.loadApp(app);
        }
    }

    private async loadApp(app: MicroApp): Promise<void> {
        try {
            // 加载应用资源
            const html = await this.fetchAppHTML(app.entry);
            const container = document.querySelector(app.container);
            
            if (container) {
                container.innerHTML = html;
                this.executeAppScripts(app);
            }
        } catch (error) {
            console.error(`Failed to load app ${app.name}:`, error);
        }
    }

    private async fetchAppHTML(entry: string): Promise<string> {
        const response = await fetch(entry);
        return await response.text();
    }

    private executeAppScripts(app: MicroApp): void {
        // 执行应用脚本
        // 这里需要处理JS隔离等问题
    }
}

// 使用示例
const microFrontend = new RouterBasedMicroFrontend([
    {
        name: 'app1',
        entry: 'http://localhost:3001',
        container: '#app1-container',
        activeRule: '/app1'
    },
    {
        name: 'app2',
        entry: 'http://localhost:3002',
        container: '#app2-container',
        activeRule: '/app2'
    }
]);

基于Web Components的实现

// web-components.ts
interface WebComponentApp {
    name: string;
    element: string;
    url: string;
}

export class WebComponentMicroFrontend {
    constructor(apps: WebComponentApp[]) {
        this.registerApps(apps);
    }

    private registerApps(apps: WebComponentApp[]): void {
        apps.forEach(app => {
            this.defineCustomElement(app);
        });
    }

    private async defineCustomElement(app: WebComponentApp): Promise<void> {
        class MicroApp extends HTMLElement {
            private shadow: ShadowRoot;

            constructor() {
                super();
                this.shadow = this.attachShadow({ mode: 'open' });
            }

            async connectedCallback() {
                try {
                    const content = await this.loadAppContent(app.url);
                    this.shadow.innerHTML = content;
                    await this.executeScripts();
                } catch (error) {
                    console.error(`Failed to load ${app.name}:`, error);
                }
            }

            private async loadAppContent(url: string): Promise<string> {
                const response = await fetch(url);
                return await response.text();
            }

            private async executeScripts(): Promise<void> {
                // 执行应用脚本，确保在Shadow DOM上下文中运行
            }
        }

        customElements.define(app.element, MicroApp);
    }
}

// 使用示例
const webComponentMicro = new WebComponentMicroFrontend([
    {
        name: 'app1',
        element: 'micro-app1',
        url: 'http://localhost:3001/app1'
    },
    {
        name: 'app2',
        element: 'micro-app2',
        url: 'http://localhost:3002/app2'
    }
]);

通信机制实现 🔄

事件总线

// event-bus.ts
type EventHandler = (data: any) => void;

export class EventBus {
    private static instance: EventBus;
    private events: Map<string, EventHandler[]>;

    private constructor() {
        this.events = new Map();
    }

    public static getInstance(): EventBus {
        if (!EventBus.instance) {
            EventBus.instance = new EventBus();
        }
        return EventBus.instance;
    }

    public on(event: string, handler: EventHandler): void {
        if (!this.events.has(event)) {
            this.events.set(event, []);
        }
        this.events.get(event)!.push(handler);
    }

    public off(event: string, handler: EventHandler): void {
        if (!this.events.has(event)) return;

        const handlers = this.events.get(event)!;
        const index = handlers.indexOf(handler);
        if (index > -1) {
            handlers.splice(index, 1);
        }
    }

    public emit(event: string, data: any): void {
        if (!this.events.has(event)) return;

        this.events.get(event)!.forEach(handler => {
            try {
                handler(data);
            } catch (error) {
                console.error(`Error in event handler for ${event}:`, error);
            }
        });
    }
}

// 使用示例
const eventBus = EventBus.getInstance();

// 在应用A中订阅事件
eventBus.on('userLogin', (user) => {
    console.log('User logged in:', user);
});

// 在应用B中触发事件
eventBus.emit('userLogin', { 
    id: 1, 
    name: 'John Doe' 
});

状态共享

// shared-state.ts
interface StateChangeListener<T> {
    (newState: T, oldState: T): void;
}

export class SharedState<T extends object> {
    private state: T;
    private listeners: StateChangeListener<T>[] = [];

    constructor(initialState: T) {
        this.state = new Proxy(initialState, {
            set: (target, property, value) => {
                const oldState = { ...this.state };
                target[property as keyof T] = value;
                this.notifyListeners(this.state, oldState);
                return true;
            }
        });
    }

    public getState(): T {
        return this.state;
    }

    public setState(partial: Partial<T>): void {
        const oldState = { ...this.state };
        Object.assign(this.state, partial);
        this.notifyListeners(this.state, oldState);
    }

    public subscribe(listener: StateChangeListener<T>): () => void {
        this.listeners.push(listener);
        return () => {
            const index = this.listeners.indexOf(listener);
            if (index > -1) {
                this.listeners.splice(index, 1);
            }
        };
    }

    private notifyListeners(newState: T, oldState: T): void {
        this.listeners.forEach(listener => {
            try {
                listener(newState, oldState);
            } catch (error) {
                console.error('Error in state change listener:', error);
            }
        });
    }
}

// 使用示例
interface UserState {
    isLoggedIn: boolean;
    user: {
        id: number;
        name: string;
    } | null;
}

const sharedState = new SharedState<UserState>({
    isLoggedIn: false,
    user: null
});

// 在应用A中订阅状态变化
sharedState.subscribe((newState, oldState) => {
    console.log('State changed:', { newState, oldState });
});

// 在应用B中更新状态
sharedState.setState({
    isLoggedIn: true,
    user: {
        id: 1,
        name: 'John Doe'
    }
});

样式隔离方案 🎨

CSS Module Federation

// style-isolation.ts
interface StyleConfig {
    prefix: string;
    scope: string;
}

export class StyleIsolation {
    private config: StyleConfig;

    constructor(config: StyleConfig) {
        this.config = config;
        this.initializeStyleIsolation();
    }

    private initializeStyleIsolation(): void {
        // 添加样式作用域
        document.documentElement.setAttribute(
            'data-app-scope',
            this.config.scope
        );

        // 处理动态添加的样式
        this.observeStyleChanges();
    }

    private observeStyleChanges(): void {
        const observer = new MutationObserver((mutations) => {
            mutations.forEach(mutation => {
                mutation.addedNodes.forEach(node => {
                    if (node instanceof HTMLStyleElement) {
                        this.processStyle(node);
                    }
                });
            });
        });

        observer.observe(document.head, {
            childList: true
        });
    }

    private processStyle(styleElement: HTMLStyleElement): void {
        const css = styleElement.textContent || '';
        const scopedCss = this.scopeCSS(css);
        styleElement.textContent = scopedCss;
    }

    private scopeCSS(css: string): string {
        // 为所有选择器添加作用域前缀
        return css.replace(/([^}]*){/g, (match) => {
            return match
                .split(',')
                .map(selector => 
                    `[data-app-scope="${this.config.scope}"] ${selector.trim()}`
                )
                .join(',');
        });
    }
}

// 使用示例
const styleIsolation = new StyleIsolation({
    prefix: 'app1',
    scope: 'micro-app1'
});

性能优化策略 ⚡

资源加载优化

// resource-loader.ts
interface ResourceConfig {
    js: string[];
    css: string[];
    prefetch?: string[];
}

export class ResourceLoader {
    private loadedResources: Set<string> = new Set();
    private loading: Map<string, Promise<void>> = new Map();

    public async loadApp(config: ResourceConfig): Promise<void> {
        try {
            // 并行加载JS和CSS资源
            await Promise.all([
                this.loadJSResources(config.js),
                this.loadCSSResources(config.css)
            ]);

            // 预加载其他资源
            if (config.prefetch) {
                this.prefetchResources(config.prefetch);
            }
        } catch (error) {
            console.error('Failed to load resources:', error);
            throw error;
        }
    }

    private async loadJSResources(urls: string[]): Promise<void> {
        const promises = urls.map(url => this.loadJS(url));
        await Promise.all(promises);
    }

    private async loadCSSResources(urls: string[]): Promise<void> {
        const promises = urls.map(url => this.loadCSS(url));
        await Promise.all(promises);
    }

    private async loadJS(url: string): Promise<void> {
        if (this.loadedResources.has(url)) {
            return;
        }

        if (this.loading.has(url)) {
            return this.loading.get(url);
        }

        const promise = new Promise<void>((resolve, reject) => {
            const script = document.createElement('script');
            script.src = url;
            script.async = true;

            script.onload = () => {
                this.loadedResources.add(url);
                this.loading.delete(url);
                resolve();
            };

            script.onerror = () => {
                this.loading.delete(url);
                reject(new Error(`Failed to load script: ${url}`));
            };

            document.head.appendChild(script);
        });

        this.loading.set(url, promise);
        return promise;
    }

    private async loadCSS(url: string): Promise<void> {
        if (this.loadedResources.has(url)) {
            return;
        }

        return new Promise((resolve, reject) => {
            const link = document.createElement('link');
            link.rel = 'stylesheet';
            link.href = url;

            link.onload = () => {
                this.loadedResources.add(url);
                resolve();
            };

            link.onerror = () => {
                reject(new Error(`Failed to load CSS: ${url}`));
            };

            document.head.appendChild(link);
        });
    }

    private prefetchResources(urls: string[]): void {
        urls.forEach(url => {
            if (!this.loadedResources.has(url)) {
                const link = document.createElement('link');
                link.rel = 'prefetch';
                link.href = url;
                document.head.appendChild(link);
            }
        });
    }
}

最佳实践建议 ⭐

应用设计原则

独立性原则
- 应用间松耦合
- 独立开发部署
- 运行时隔离
- 故障隔离
统一规范
- 通信协议标准
- 路由管理规范
- 样式命名规范
- 错误处理机制
性能优化
- 按需加载策略
- 资源复用机制
- 缓存优化方案
- 预加载策略

开发流程建议

项目初始化

# 创建微前端项目结构
mkdir micro-frontend && cd micro-frontend
mkdir container app1 app2 shared

# 初始化基座应用
cd container
npm init -y
npm install @micro-frontend/core

# 初始化子应用
cd ../app1
npm init -y
npm install @micro-frontend/app

开发规范

// 子应用生命周期规范
interface MicroAppLifecycle {
    bootstrap(): Promise<void>;
    mount(props: Record<string, any>): Promise<void>;
    unmount(): Promise<void>;
}

// 实现示例
export class MicroApp implements MicroAppLifecycle {
    async bootstrap(): Promise<void> {
        // 应用初始化
    }

    async mount(props: Record<string, any>): Promise<void> {
        // 应用挂载
    }

    async unmount(): Promise<void> {
        // 应用卸载
    }
}