来源：李永宁

https://juejin.im/post/6862661545592111111

前序

目的

• 会使用single-spa开发项目，然后打包部署上线

• 刨析single-spa的源码原理

• 手写一个自己的single-spa框架

过程

• 编写示例项目

• 打包部署

• 框架源码解读

• 手写框架

关于微前端的介绍这里就不再赘述了，网上有很多的文章，本文的重点在于刨析微前端框架single-spa的实现原理。

single-spa是一个很好的微前端基础框架，qiankun框架就是基于single-spa来实现的，在single-spa的基础上做了一层封装，也解决了single-spa的一些缺陷。

因为single-spa是一个基础的微前端框架，了解了它的实现原理，再去看其它的微前端框架，就会非常容易了。

提示

• 先熟悉基本使用，熟悉常用的API，可通过示例项目 + 官网相结合来达成

• 如果基础比较好，可以先读后面的手写 single-spa 框架部分，再回来阅读源码，效果可能会更好

• 文章中涉及到的所有代码都在 github: https://github.com/liyongning/micro-frontend.git（示例项目 + single-spa源码分析 + 手写single-spa框架 + single-spa-vue源码分析）

示例项目

新建项目目录，接下来的所有代码都会在该目录中完成

mkdir micro-frontend && cd micro-frontend

示例代码都是通过vue来编写的，当然也可以采用其它的，比如react或者原生JS等

子应用 app1

新建子应用

vue create app1

按图选择，去除一切项目不需要的干扰项，后面一路回车，等待应用创建完毕

配置子应用

以下所有的操作都在项目根目录/micro-frontend/app1下完成

vue.config.js

在项目根目录下新建vue.config.js文件

const package = require('./package.json')
module.exports = {// 告诉子应用在这个地址加载静态资源，否则会去基座应用的域名下加载publicPath: '//localhost:8081',// 开发服务器devServer: {port: 8081},configureWebpack: {// 导出umd格式的包，在全局对象上挂载属性package.name，基座应用需要通过这个全局对象获取一些信息，比如子应用导出的生命周期函数output: {// library的值在所有子应用中需要唯一library: package.name,libraryTarget: 'umd'}}
}

安装single-spa-vue

npm i single-spa-vue -S

single-spa-vue负责为vue应用生成通用的生命周期钩子，在子应用注册到single-spa的基座应用时需要用到

改造入口文件

// /src/main.js
import Vue from 'vue'
import App from './App.vue'
import router from './router'
import singleSpaVue from 'single-spa-vue'Vue.config.productionTip = falseconst appOptions = {el: '#microApp',router,render: h => h(App)
}// 支持应用独立运行、部署，不依赖于基座应用
if (!window.singleSpaNavigate) {delete appOptions.elnew Vue(appOptions).$mount('#app')
}// 基于基座应用，导出生命周期函数
const vueLifecycle = singleSpaVue({Vue,appOptions
})export function bootstrap (props) {console.log('app1 bootstrap')return vueLifecycle.bootstrap(() => {})
}export function mount (props) {console.log('app1 mount')return vueLifecycle.mount(() => {})
}export function unmount (props) {console.log('app1 unmount')return vueLifecycle.unmount(() => {})
}

更改视图文件

<!-- /views/Home.vue -->
<template><div class="home"><h1>app1 home page</h1></div>
</template>

<!-- /views/About.vue -->
<template><div class="about"><h1>app1 about page</h1></div>
</template>

环境配置文件

.env

应用独立运行时的开发环境配置

NODE_ENV=development
VUE_APP_BASE_URL=/

.env.micro

作为子应用运行时的开发环境配置

NODE_ENV=development
VUE_APP_BASE_URL=/app1

.env.buildMicro

作为子应用构建生产环境bundle时的环境配置，但这里的NODE_ENV为development，而不是production，是为了方便，这个方便其实single-spa带来的弊端（js entry的弊端）

NODE_ENV=development
VUE_APP_BASE_URL=/app1

修改路由文件

// /src/router/index.js
// ...
const router = new VueRouter({mode: 'history',// 通过环境变量来配置路由的 base urlbase: process.env.VUE_APP_BASE_URL,routes
})
// ...

修改package.json中的script

{"name": "app1",// ..."scripts": {// 独立运行"serve": "vue-cli-service serve",// 作为子应用运行"serve:micro": "vue-cli-service serve --mode micro",// 构建子应用"build": "vue-cli-service build --mode buildMicro"},// ...
}

启动应用

应用独立运行

npm run serve

当然下面的启动方式也可以，只不过会在pathname的开头加了/app1前缀

npm run serve:micro

作为子应用运行

npm run serve:micro

作为独立应用访问

子应用 app2

在/micro-frontend目录下新建子应用app2，步骤同app1，只需把过程中出现的'app1'字样改成'app2'即可，vue.config.js中的8081改成8082`

启动应用，作为独立应用访问

基座应用 layout

在/micro-frontend目录下新建基座应用，为了简洁明了，新建项目时选择的配置项和子应用一样；在本示例中基座应用采用了vue来实现，用别的方式或者框架实现也可以，比如自己用webpack构建一个项目。

以下操作都在/micro-frontend/layout目录下进行

安装single-spa

npm i single-spa -S

改造基座项目

入口文件

// src/main.js
import Vue from 'vue'
import App from './App.vue'
import router from './router'
import { registerApplication, start } from 'single-spa'Vue.config.productionTip = false// 远程加载子应用
function createScript(url) {return new Promise((resolve, reject) => {const script = document.createElement('script')script.src = urlscript.onload = resolvescript.onerror = rejectconst firstScript = document.getElementsByTagName('script')[0]firstScript.parentNode.insertBefore(script, firstScript)})
}// 记载函数，返回一个 promise
function loadApp(url, globalVar) {// 支持远程加载子应用return async () => {await createScript(url + '/js/chunk-vendors.js')await createScript(url + '/js/app.js')// 这里的return很重要，需要从这个全局对象中拿到子应用暴露出来的生命周期函数return window[globalVar]}
}// 子应用列表
const apps = [{// 子应用名称name: 'app1',// 子应用加载函数，是一个promiseapp: loadApp('http://localhost:8081', 'app1'),// 当路由满足条件时（返回true），激活（挂载）子应用activeWhen: location => location.pathname.startsWith('/app1'),// 传递给子应用的对象customProps: {}},{name: 'app2',app: loadApp('http://localhost:8082', 'app2'),activeWhen: location => location.pathname.startsWith('/app2'),customProps: {}},
]// 注册子应用
for (let i = apps.length - 1; i >= 0; i--) {registerApplication(apps[i])
}new Vue({router,mounted() {// 启动start()},render: h => h(App)
}).$mount('#app')

App.vue

<template><div id="app"><div id="nav"><router-link to="/app1">app1</router-link> |<router-link to="/app2">app2</router-link></div><!-- 子应用容器 --><div id = "microApp"><router-view/></div></div>
</template><style>
#app {font-family: Avenir, Helvetica, Arial, sans-serif;-webkit-font-smoothing: antialiased;-moz-osx-font-smoothing: grayscale;text-align: center;color: #2c3e50;
}#nav {padding: 30px;
}#nav a {font-weight: bold;color: #2c3e50;
}#nav a.router-link-exact-active {color: #42b983;
}
</style>

路由

import Vue from 'vue'
import VueRouter from 'vue-router'Vue.use(VueRouter)const routes = []const router = new VueRouter({mode: 'history',base: process.env.BASE_URL,routes
})export default router

启动基座应用

npm run serve

浏览器访问基座应用

终于看到了结果。

小技巧

有时候single-spa可能会报一些我们现在无法理解的错误，我们可能需要去做代码调试，阅读源码时碰到不理解的地方也需要编写示例 + 单步调试，但是默认的是已经打包压缩后的代码，不太方便做这些，大家可以在node_modules目录找到single-spa目录，把目录下的package.json中的module字段的值改为lib/single-spa.dev.js，这是一个未压缩的bundle，利于代码的阅读的调试，当然需要重启应用。

子应用也是一样类似的技巧，因为single-spa-vue就一个文件，可以直接拷贝出来放到项目的/src目录下，将main.js中的引入的single-spa-vue改成当前目录即可。

打包部署

打包

在各个项目的根目录下分别执行

npm run build

部署

可以将打包后的bundle发布到nginx服务器上，这个nginx服务器可以是单独的服务器、或者虚拟机、亦或是docker容器都行，这里采用serve在本地模拟部署

如果你有条件部署到nginx上，需要注意nginx的代理配置

• 对于子应用静态资源的加载只需要拦截相应的前缀将请求转发到对应子应用的目录下即可

• 页面刷新只需要拦截到主应用即可，主应用内部自己根据activeWhen去挂载对应的子应用

全局安装 serve

npm i serve -g

在各个项目的根目录下启动 serve

serve ./dist -p port

在浏览器访问基座应用的地址，发现得到和刚才一样的结果

single-spa 源码分析

整个阅读过程以示例项目为例，阅读源码时一定要多动手写注释、做笔记，遇到不理解的地方编写示例代码 + console.log + 单步调试，切记不要只看不动手。

single-spa 源码阅读思维导图

这是我在阅读时整理的一个思维导图，源码中也写了大量的注释，大家可以参照着进行阅读。Ok ！！这就开始吧

从源码目录中可以看到，single-spa是使用rollup来打包的，从rollup.config.js中可以发现入口是single-spa.js， 打开会发现里面导出了一大堆东西，有我们非常熟悉的各个方法，我们就从registerApplication方法开始

registerApplication 注册子应用

single-spa/src/applications/apps.js

/*** 注册应用，两种方式* registerApplication('app1', loadApp(url), activeWhen('/app1'), customProps)* registerApplication({*    name: 'app1',*    app: loadApp(url),*    activeWhen: activeWhen('/app1'),*    customProps: {}* })* @param {*} appNameOrConfig 应用名称或者应用配置对象* @param {*} appOrLoadApp 应用的加载方法，是一个 promise* @param {*} activeWhen 判断应用是否激活的一个方法，方法返回 true or false* @param {*} customProps 传递给子应用的 props 对象*/
export function registerApplication(appNameOrConfig,appOrLoadApp,activeWhen,customProps
) {/*** 格式化用户传递的应用配置参数* registration = {*    name: 'app1',*    loadApp: 返回promise的函数,*    activeWhen: 返回boolean值的函数,*    customProps: {},* }*/const registration = sanitizeArguments(appNameOrConfig,appOrLoadApp,activeWhen,customProps);// 判断应用是否重名if (getAppNames().indexOf(registration.name) !== -1)throw Error(formatErrorMessage(21,__DEV__ &&`There is already an app registered with name ${registration.name}`,registration.name));// 将各个应用的配置信息都存放到 apps 数组中apps.push(// 给每个应用增加一个内置属性assign({loadErrorTime: null,// 最重要的，应用的状态status: NOT_LOADED,parcels: {},devtools: {overlays: {options: {},selectors: [],},},},registration));// 浏览器环境运行if (isInBrowser) {// https://zh-hans.single-spa.js.org/docs/api#ensurejquerysupport// 如果页面中使用了jQuery，则给jQuery打patchensureJQuerySupport();reroute();}
}

sanitizeArguments 格式化用户传递的子应用配置参数

single-spa/src/applications/apps.js

// 返回处理后的应用配置对象
function sanitizeArguments(appNameOrConfig,appOrLoadApp,activeWhen,customProps
) {// 判断第一个参数是否为对象const usingObjectAPI = typeof appNameOrConfig === "object";// 初始化应用配置对象const registration = {name: null,loadApp: null,activeWhen: null,customProps: null,};if (usingObjectAPI) {// 注册应用的时候传递的参数是对象validateRegisterWithConfig(appNameOrConfig);registration.name = appNameOrConfig.name;registration.loadApp = appNameOrConfig.app;registration.activeWhen = appNameOrConfig.activeWhen;registration.customProps = appNameOrConfig.customProps;} else {// 参数列表validateRegisterWithArguments(appNameOrConfig,appOrLoadApp,activeWhen,customProps);registration.name = appNameOrConfig;registration.loadApp = appOrLoadApp;registration.activeWhen = activeWhen;registration.customProps = customProps;}// 如果第二个参数不是一个函数，比如是一个包含已经生命周期的对象，则包装成一个返回 promise 的函数registration.loadApp = sanitizeLoadApp(registration.loadApp);// 如果用户没有提供 props 对象，则给一个默认的空对象registration.customProps = sanitizeCustomProps(registration.customProps);// 保证activeWhen是一个返回boolean值的函数registration.activeWhen = sanitizeActiveWhen(registration.activeWhen);// 返回处理后的应用配置对象return registration;
}

validateRegisterWithConfig

single-spa/src/applications/apps.js

/*** 验证应用配置对象的各个属性是否存在不合法的情况，存在则抛出错误* @param {*} config = { name: 'app1', app: function, activeWhen: function, customProps: {} }*/
export function validateRegisterWithConfig(config) {// 异常判断，应用的配置对象不能是数组或者nullif (Array.isArray(config) || config === null)throw Error(formatErrorMessage(39,__DEV__ && "Configuration object can't be an Array or null!"));// 配置对象只能包括这四个keyconst validKeys = ["name", "app", "activeWhen", "customProps"];// 找到配置对象存在的无效的keyconst invalidKeys = Object.keys(config).reduce((invalidKeys, prop) =>validKeys.indexOf(prop) >= 0 ? invalidKeys : invalidKeys.concat(prop),[]);// 如果存在无效的key，则抛出一个错误if (invalidKeys.length !== 0)throw Error(formatErrorMessage(38,__DEV__ &&`The configuration object accepts only: ${validKeys.join(", ")}. Invalid keys: ${invalidKeys.join(", ")}.`,validKeys.join(", "),invalidKeys.join(", ")));// 验证应用名称，只能是字符串，且不能为空if (typeof config.name !== "string" || config.name.length === 0)throw Error(formatErrorMessage(20,__DEV__ &&"The config.name on registerApplication must be a non-empty string"));// app 属性只能是一个对象或者函数// 对象是一个已被解析过的对象，是一个包含各个生命周期的对象；// 加载函数必须返回一个 promise// 以上信息在官方文档中有提到：https://zh-hans.single-spa.js.org/docs/configurationif (typeof config.app !== "object" && typeof config.app !== "function")throw Error(formatErrorMessage(20,__DEV__ &&"The config.app on registerApplication must be an application or a loading function"));// 第三个参数，可以是一个字符串，也可以是一个函数，也可以是两者组成的一个数组，表示当前应该被激活的应用的baseURLconst allowsStringAndFunction = (activeWhen) =>typeof activeWhen === "string" || typeof activeWhen === "function";if (!allowsStringAndFunction(config.activeWhen) &&!(Array.isArray(config.activeWhen) &&config.activeWhen.every(allowsStringAndFunction)))throw Error(formatErrorMessage(24,__DEV__ &&"The config.activeWhen on registerApplication must be a string, function or an array with both"));// 传递给子应用的props对象必须是一个对象if (!validCustomProps(config.customProps))throw Error(formatErrorMessage(22,__DEV__ && "The optional config.customProps must be an object"));
}

validateRegisterWithArguments

single-spa/src/applications/apps.js

// 同样是验证四个参数是否合法
function validateRegisterWithArguments(name,appOrLoadApp,activeWhen,customProps
) {if (typeof name !== "string" || name.length === 0)throw Error(formatErrorMessage(20,__DEV__ &&`The 1st argument to registerApplication must be a non-empty string 'appName'`));if (!appOrLoadApp)throw Error(formatErrorMessage(23,__DEV__ &&"The 2nd argument to registerApplication must be an application or loading application function"));if (typeof activeWhen !== "function")throw Error(formatErrorMessage(24,__DEV__ &&"The 3rd argument to registerApplication must be an activeWhen function"));if (!validCustomProps(customProps))throw Error(formatErrorMessage(22,__DEV__ &&"The optional 4th argument is a customProps and must be an object"));
}

sanitizeLoadApp

single-spa/src/applications/apps.js

// 保证第二个参数一定是一个返回 promise 的函数
function sanitizeLoadApp(loadApp) {if (typeof loadApp !== "function") {return () => Promise.resolve(loadApp);}return loadApp;
}

sanitizeCustomProps

single-spa/src/applications/apps.js

// 保证 props 不为 undefined
function sanitizeCustomProps(customProps) {return customProps ? customProps : {};
}

sanitizeActiveWhen

single-spa/src/applications/apps.js

// 得到一个函数，函数负责判断浏览器当前地址是否和用户给定的baseURL相匹配，匹配返回true，否则返回false
function sanitizeActiveWhen(activeWhen) {// []let activeWhenArray = Array.isArray(activeWhen) ? activeWhen : [activeWhen];// 保证数组中每个元素都是一个函数activeWhenArray = activeWhenArray.map((activeWhenOrPath) =>typeof activeWhenOrPath === "function"? activeWhenOrPath// activeWhen如果是一个路径，则保证成一个函数: pathToActiveWhen(activeWhenOrPath));// 返回一个函数，函数返回一个 boolean 值return (location) =>activeWhenArray.some((activeWhen) => activeWhen(location));
}

pathToActiveWhen

single-spa/src/applications/apps.js

export function pathToActiveWhen(path) {// 根据用户提供的baseURL，生成正则表达式const regex = toDynamicPathValidatorRegex(path);// 函数返回boolean值，判断当前路由是否匹配用户给定的路径return (location) => {const route = location.href.replace(location.origin, "").replace(location.search, "").split("?")[0];return regex.test(route);};
}

reroute 更改app.status和执行生命周期函数

single-spa/src/navigation/reroute.js

/*** 每次切换路由前，将应用分为4大类，* 首次加载时执行loadApp* 后续的路由切换执行performAppChange* 为四大类的应用分别执行相应的操作，比如更改app.status，执行生命周期函数* 所以，从这里也可以看出来，single-spa就是一个维护应用的状态机* @param {*} pendingPromises * @param {*} eventArguments */
export function reroute(pendingPromises = [], eventArguments) {// 应用正在切换，这个状态会在执行performAppChanges之前置为true，执行结束之后再置为false// 如果在中间用户重新切换路由了，即走这个if分支，暂时看起来就在数组中存储了一些信息，没看到有什么用// 字面意思理解就是用户等待app切换if (appChangeUnderway) {return new Promise((resolve, reject) => {peopleWaitingOnAppChange.push({resolve,reject,eventArguments,});});}// 将应用分为4大类const {// 需要被移除的appsToUnload,// 需要被卸载的appsToUnmount,// 需要被加载的appsToLoad,// 需要被挂载的appsToMount,} = getAppChanges();let appsThatChanged;// 是否已经执行 start 方法if (isStarted()) {// 已执行appChangeUnderway = true;// 所有需要被改变的的应用appsThatChanged = appsToUnload.concat(appsToLoad,appsToUnmount,appsToMount);// 执行改变return performAppChanges();} else {// 未执行appsThatChanged = appsToLoad;// 加载Appsreturn loadApps();}// 整体返回一个立即resolved的promise，通过微任务来加载appsfunction loadApps() {return Promise.resolve().then(() => {// 加载每个子应用，并做一系列的状态变更和验证（比如结果为promise、子应用要导出生命周期函数）const loadPromises = appsToLoad.map(toLoadPromise);return (// 保证所有加载子应用的微任务执行完成Promise.all(loadPromises).then(callAllEventListeners)// there are no mounted apps, before start() is called, so we always return [].then(() => []).catch((err) => {callAllEventListeners();throw err;}));});}function performAppChanges() {return Promise.resolve().then(() => {// https://github.com/single-spa/single-spa/issues/545// 自定义事件，在应用状态发生改变之前可触发，给用户提供搞事情的机会window.dispatchEvent(new CustomEvent(appsThatChanged.length === 0? "single-spa:before-no-app-change": "single-spa:before-app-change",getCustomEventDetail(true)));window.dispatchEvent(new CustomEvent("single-spa:before-routing-event",getCustomEventDetail(true)));// 移除应用 => 更改应用状态，执行unload生命周期函数，执行一些清理动作// 其实一般情况下这里没有真的移除应用const unloadPromises = appsToUnload.map(toUnloadPromise);// 卸载应用，更改状态，执行unmount生命周期函数const unmountUnloadPromises = appsToUnmount.map(toUnmountPromise)// 卸载完然后移除，通过注册微任务的方式实现.map((unmountPromise) => unmountPromise.then(toUnloadPromise));const allUnmountPromises = unmountUnloadPromises.concat(unloadPromises);const unmountAllPromise = Promise.all(allUnmountPromises);// 卸载全部完成后触发一个事件unmountAllPromise.then(() => {window.dispatchEvent(new CustomEvent("single-spa:before-mount-routing-event",getCustomEventDetail(true)));});/* We load and bootstrap apps while other apps are unmounting, but we* wait to mount the app until all apps are finishing unmounting* 这个原因其实是因为这些操作都是通过注册不同的微任务实现的，而JS是单线程执行，* 所以自然后续的只能等待前面的执行完了才能执行* 这里一般情况下其实不会执行，只有手动执行了unloadApplication方法才会二次加载*/const loadThenMountPromises = appsToLoad.map((app) => {return toLoadPromise(app).then((app) =>tryToBootstrapAndMount(app, unmountAllPromise));});/* These are the apps that are already bootstrapped and just need* to be mounted. They each wait for all unmounting apps to finish up* before they mount.* 初始化和挂载app，其实做的事情很简单，就是改变app.status，执行生命周期函数* 当然这里的初始化和挂载其实是前后脚一起完成的(只要中间用户没有切换路由)*/const mountPromises = appsToMount.filter((appToMount) => appsToLoad.indexOf(appToMount) < 0).map((appToMount) => {return tryToBootstrapAndMount(appToMount, unmountAllPromise);});// 后面就没啥了，可以理解为收尾工作return unmountAllPromise.catch((err) => {callAllEventListeners();throw err;}).then(() => {/* Now that the apps that needed to be unmounted are unmounted, their DOM navigation* events (like hashchange or popstate) should have been cleaned up. So it's safe* to let the remaining captured event listeners to handle about the DOM event.*/callAllEventListeners();return Promise.all(loadThenMountPromises.concat(mountPromises)).catch((err) => {pendingPromises.forEach((promise) => promise.reject(err));throw err;}).then(finishUpAndReturn);});});}
}

getAppChanges

single-spa/src/applications/apps.js

// 将应用分为四大类
export function getAppChanges() {// 需要被移除的应用const appsToUnload = [],// 需要被卸载的应用appsToUnmount = [],// 需要被加载的应用appsToLoad = [],// 需要被挂载的应用appsToMount = [];// We re-attempt to download applications in LOAD_ERROR after a timeout of 200 millisecondsconst currentTime = new Date().getTime();apps.forEach((app) => {// boolean，应用是否应该被激活const appShouldBeActive =app.status !== SKIP_BECAUSE_BROKEN && shouldBeActive(app);switch (app.status) {// 需要被加载的应用case LOAD_ERROR:if (currentTime - app.loadErrorTime >= 200) {appsToLoad.push(app);}break;// 需要被加载的应用case NOT_LOADED:case LOADING_SOURCE_CODE:if (appShouldBeActive) {appsToLoad.push(app);}break;// 状态为xx的应用case NOT_BOOTSTRAPPED:case NOT_MOUNTED:if (!appShouldBeActive && getAppUnloadInfo(toName(app))) {// 需要被移除的应用appsToUnload.push(app);} else if (appShouldBeActive) {// 需要被挂载的应用appsToMount.push(app);}break;// 需要被卸载的应用，已经处于挂载状态，但现在路由已经变了的应用需要被卸载case MOUNTED:if (!appShouldBeActive) {appsToUnmount.push(app);}break;// all other statuses are ignored}});return { appsToUnload, appsToUnmount, appsToLoad, appsToMount };
}

shouldBeActive

single-spa/src/applications/app.helpers.js

// 返回boolean值，应用是否应该被激活
export function shouldBeActive(app) {try {return app.activeWhen(window.location);} catch (err) {handleAppError(err, app, SKIP_BECAUSE_BROKEN);return false;}
}

toLoadPromise

single-spa/src/lifecycles/load.js

/*** 通过微任务加载子应用，其实singleSpa中很多地方都用了微任务* 这里最终是return了一个promise出行，在注册了加载子应用的微任务* 概括起来就是：*  更改app.status为LOAD_SOURCE_CODE => NOT_BOOTSTRAP，当然还有可能是LOAD_ERROR*  执行加载函数，并将props传递给加载函数，给用户处理props的一个机会,因为这个props是一个完备的props*  验证加载函数的执行结果，必须为promise，且加载函数内部必须return一个对象*  这个对象是子应用的，对象中必须包括各个必须的生命周期函数*  然后将生命周期方法通过一个函数包裹并挂载到app对象上*  app加载完成，删除app.loadPromise* @param {*} app */
export function toLoadPromise(app) {return Promise.resolve().then(() => {if (app.loadPromise) {// 说明app已经在被加载return app.loadPromise;}// 只有状态为NOT_LOADED和LOAD_ERROR的app才可以被加载if (app.status !== NOT_LOADED && app.status !== LOAD_ERROR) {return app;}// 设置App的状态app.status = LOADING_SOURCE_CODE;let appOpts, isUserErr;return (app.loadPromise = Promise.resolve().then(() => {// 执行app的加载函数，并给子应用传递props => 用户自定义的customProps和内置的比如应用的名称、singleSpa实例// 其实这里有个疑问，这个props是怎么传递给子应用的，感觉跟后面的生命周期函数有关const loadPromise = app.loadApp(getProps(app));// 加载函数需要返回一个promiseif (!smellsLikeAPromise(loadPromise)) {// The name of the app will be prepended to this error message inside of the handleAppError functionisUserErr = true;throw Error(formatErrorMessage(33,__DEV__ &&`single-spa loading function did not return a promise. Check the second argument to registerApplication('${toName(app)}', loadingFunction, activityFunction)`,toName(app)));}// 这里很重要，这个val就是示例项目中加载函数中return出来的window.singleSpa，这个属性是子应用打包时设置的return loadPromise.then((val) => {app.loadErrorTime = null;// window.singleSpaappOpts = val;let validationErrMessage, validationErrCode;// 以下进行一系列的验证，已window.singleSpa为例说明，简称g.s// g.s必须为对象if (typeof appOpts !== "object") {validationErrCode = 34;if (__DEV__) {validationErrMessage = `does not export anything`;}}// g.s必须导出bootstrap生命周期函数if (!validLifecycleFn(appOpts.bootstrap)) {validationErrCode = 35;if (__DEV__) {validationErrMessage = `does not export a bootstrap function or array of functions`;}}// g.s必须导出mount生命周期函数if (!validLifecycleFn(appOpts.mount)) {validationErrCode = 36;if (__DEV__) {validationErrMessage = `does not export a bootstrap function or array of functions`;}}// g.s必须导出unmount生命周期函数if (!validLifecycleFn(appOpts.unmount)) {validationErrCode = 37;if (__DEV__) {validationErrMessage = `does not export a bootstrap function or array of functions`;}}const type = objectType(appOpts);// 说明上述验证失败，抛出错误提示信息if (validationErrCode) {let appOptsStr;try {appOptsStr = JSON.stringify(appOpts);} catch {}console.error(formatErrorMessage(validationErrCode,__DEV__ &&`The loading function for single-spa ${type} '${toName(app)}' resolved with the following, which does not have bootstrap, mount, and unmount functions`,type,toName(app),appOptsStr),appOpts);handleAppError(validationErrMessage, app, SKIP_BECAUSE_BROKEN);return app;}if (appOpts.devtools && appOpts.devtools.overlays) {// app.devtoolsoverlays添加子应用的devtools.overlays的属性，不知道是干嘛用的app.devtools.overlays = assign({},app.devtools.overlays,appOpts.devtools.overlays);}// 设置app状态为未初始化，表示加载完了app.status = NOT_BOOTSTRAPPED;// 在app对象上挂载生命周期方法，每个方法都接收一个props作为参数，方法内部执行子应用导出的生命周期函数，并确保生命周期函数返回一个promiseapp.bootstrap = flattenFnArray(appOpts, "bootstrap");app.mount = flattenFnArray(appOpts, "mount");app.unmount = flattenFnArray(appOpts, "unmount");app.unload = flattenFnArray(appOpts, "unload");app.timeouts = ensureValidAppTimeouts(appOpts.timeouts);// 执行到这里说明子应用已成功加载，删除app.loadPromise属性delete app.loadPromise;return app;});}).catch((err) => {// 加载失败，稍后重新加载delete app.loadPromise;let newStatus;if (isUserErr) {newStatus = SKIP_BECAUSE_BROKEN;} else {newStatus = LOAD_ERROR;app.loadErrorTime = new Date().getTime();}handleAppError(err, app, newStatus);return app;}));});
}

getProps

single-spa/src/lifecycles/prop.helpers.js

/*** 得到传递给子应用的props* @param {} appOrParcel => app * 以下返回内容其实在官网也都有提到，比如singleSpa实例，目的是为了子应用不需要重复引入single-spa* return {*    ...customProps,*    name,*    mountParcel: mountParcel.bind(appOrParcel),*    singleSpa, * }*/
export function getProps(appOrParcel) {// app.nameconst name = toName(appOrParcel);// app.customProps，以下对customProps对象的判断逻辑有点多余// 因为前面的参数格式化已经保证customProps肯定是一个对象let customProps =typeof appOrParcel.customProps === "function"? appOrParcel.customProps(name, window.location): appOrParcel.customProps;if (typeof customProps !== "object" ||customProps === null ||Array.isArray(customProps)) {customProps = {};console.warn(formatErrorMessage(40,__DEV__ &&`single-spa: ${name}'s customProps function must return an object. Received ${customProps}`),name,customProps);}const result = assign({}, customProps, {name,mountParcel: mountParcel.bind(appOrParcel),singleSpa,});if (isParcel(appOrParcel)) {result.unmountSelf = appOrParcel.unmountThisParcel;}return result;
}

smellsLikeAPromise

single-spa/src/lifecycles/lifecycle.helpers.js

// 判断一个变量是否为promise
export function smellsLikeAPromise(promise) {return (promise &&typeof promise.then === "function" &&typeof promise.catch === "function");
}

flattenFnArray

single-spa/src/lifecycles/lifecycle.helpers.js

/*** 返回一个接受props作为参数的函数，这个函数负责执行子应用中的生命周期函数，* 并确保生命周期函数返回的结果为promise* @param {*} appOrParcel => window.singleSpa，子应用打包后的对象* @param {*} lifecycle => 字符串，生命周期名称*/
export function flattenFnArray(appOrParcel, lifecycle) {// fns = fn or []let fns = appOrParcel[lifecycle] || [];// fns = [] or [fn]fns = Array.isArray(fns) ? fns : [fns];// 有些生命周期函数子应用可能不会设置，比如unloadif (fns.length === 0) {fns = [() => Promise.resolve()];}const type = objectType(appOrParcel);const name = toName(appOrParcel);return function (props) {// 这里最后返回了一个promise链，这个操作似乎没啥必要，因为不可能出现同名的生命周期函数，所以，这里将生命周期函数放数组，没太理解目的是啥return fns.reduce((resultPromise, fn, index) => {return resultPromise.then(() => {// 执行生命周期函数，传递props给函数，并验证函数的返回结果，必须为promiseconst thisPromise = fn(props);return smellsLikeAPromise(thisPromise)? thisPromise: Promise.reject(formatErrorMessage(15,__DEV__ &&`Within ${type} ${name}, the lifecycle function ${lifecycle} at array index ${index} did not return a promise`,type,name,lifecycle,index));});}, Promise.resolve());};
}

toUnloadPromise

single-spa/src/lifecycles/unload.js

const appsToUnload = {};
/*** 移除应用，就更改一下应用的状态，执行unload生命周期函数，执行清理操作* * 其实一般情况是不会执行移除操作的，除非你手动调用unloadApplication方法* 单步调试会发现appsToUnload对象是个空对象，所以第一个if就return了，这里啥也没做* https://zh-hans.single-spa.js.org/docs/api#unloadapplication* */
export function toUnloadPromise(app) {return Promise.resolve().then(() => {// 应用信息const unloadInfo = appsToUnload[toName(app)];if (!unloadInfo) {/* No one has called unloadApplication for this app,* 不需要移除* 一般情况下都不需要移除，只有在调用unloadApplication方法手动执行移除时才会* 执行后面的内容*/return app;}// 已经卸载了，执行一些清理操作if (app.status === NOT_LOADED) {/* This app is already unloaded. We just need to clean up* anything that still thinks we need to unload the app.*/finishUnloadingApp(app, unloadInfo);return app;}// 如果应用正在执行挂载，路由突然发生改变，那么也需要应用挂载完成才可以执行移除if (app.status === UNLOADING) {/* Both unloadApplication and reroute want to unload this app.* It only needs to be done once, though.*/return unloadInfo.promise.then(() => app);}if (app.status !== NOT_MOUNTED) {/* The app cannot be unloaded until it is unmounted.*/return app;}// 更改状态为 UNLOADINGapp.status = UNLOADING;// 在合理的时间范围内执行生命周期函数return reasonableTime(app, "unload").then(() => {// 一些清理操作finishUnloadingApp(app, unloadInfo);return app;}).catch((err) => {errorUnloadingApp(app, unloadInfo, err);return app;});});
}

finishUnloadingApp

single-spa/src/lifecycles/unload.js

// 移除完成，执行一些清理动作，其实就是从appsToUnload数组中移除该app，移除生命周期函数，更改app.status
// 但应用不是真的被移除，后面再激活时不需要重新去下载资源,，只是做一些状态上的变更，当然load的那个过程还是需要的，这点可能需要再确认一下
function finishUnloadingApp(app, unloadInfo) {delete appsToUnload[toName(app)];// Unloaded apps don't have lifecyclesdelete app.bootstrap;delete app.mount;delete app.unmount;delete app.unload;app.status = NOT_LOADED;/* resolve the promise of whoever called unloadApplication.* This should be done after all other cleanup/bookkeeping*/unloadInfo.resolve();
}

reasonableTime

single-spa/src/applications/timeouts.js

/*** 合理的时间，即生命周期函数合理的执行时间* 在合理的时间内执行生命周期函数，并将函数的执行结果resolve出去* @param {*} appOrParcel => app* @param {*} lifecycle => 生命周期函数名*/
export function reasonableTime(appOrParcel, lifecycle) {// 应用的超时配置const timeoutConfig = appOrParcel.timeouts[lifecycle];// 超时警告const warningPeriod = timeoutConfig.warningMillis;const type = objectType(appOrParcel);return new Promise((resolve, reject) => {let finished = false;let errored = false;// 这里很关键，之前一直奇怪props是怎么传递给子应用的，这里就是了，果然和之前的猜想是一样的// 是在执行生命周期函数时像子应用传递的props，所以之前执行loadApp传递props不会到子应用，// 那么设计估计是给用户自己处理props的一个机会吧，因为那个时候处理的props已经是{ ...customProps, ...内置props }appOrParcel[lifecycle](getProps(appOrParcel)).then((val) => {finished = true;resolve(val);}).catch((val) => {finished = true;reject(val);});// 下面就没啥了，就是超时的一些提示信息setTimeout(() => maybeTimingOut(1), warningPeriod);setTimeout(() => maybeTimingOut(true), timeoutConfig.millis);const errMsg = formatErrorMessage(31,__DEV__ &&`Lifecycle function ${lifecycle} for ${type} ${toName(appOrParcel)} lifecycle did not resolve or reject for ${timeoutConfig.millis} ms.`,lifecycle,type,toName(appOrParcel),timeoutConfig.millis);function maybeTimingOut(shouldError) {if (!finished) {if (shouldError === true) {errored = true;if (timeoutConfig.dieOnTimeout) {reject(Error(errMsg));} else {console.error(errMsg);//don't resolve or reject, we're waiting this one out}} else if (!errored) {const numWarnings = shouldError;const numMillis = numWarnings * warningPeriod;console.warn(errMsg);if (numMillis + warningPeriod < timeoutConfig.millis) {setTimeout(() => maybeTimingOut(numWarnings + 1), warningPeriod);}}}}});
}

toUnmountPromise

single-spa/src/lifecycles/unmount.js

/*** 执行了状态上的更改* 执行unmount生命周期函数* @param {*} appOrParcel => app* @param {*} hardFail => 索引*/
export function toUnmountPromise(appOrParcel, hardFail) {return Promise.resolve().then(() => {// 只卸载已挂载的应用if (appOrParcel.status !== MOUNTED) {return appOrParcel;}// 更改状态appOrParcel.status = UNMOUNTING;// 有关parcels的一些处理，没使用过parcels，所以unmountChildrenParcels = []const unmountChildrenParcels = Object.keys(appOrParcel.parcels).map((parcelId) => appOrParcel.parcels[parcelId].unmountThisParcel());let parcelError;return Promise.all(unmountChildrenParcels)// 在合理的时间范围内执行unmount生命周期函数.then(unmountAppOrParcel, (parcelError) => {// There is a parcel unmount errorreturn unmountAppOrParcel().then(() => {// Unmounting the app/parcel succeeded, but unmounting its children parcels did notconst parentError = Error(parcelError.message);if (hardFail) {throw transformErr(parentError, appOrParcel, SKIP_BECAUSE_BROKEN);} else {handleAppError(parentError, appOrParcel, SKIP_BECAUSE_BROKEN);}});}).then(() => appOrParcel);function unmountAppOrParcel() {// We always try to unmount the appOrParcel, even if the children parcels failed to unmount.return reasonableTime(appOrParcel, "unmount").then(() => {// The appOrParcel needs to stay in a broken status if its children parcels fail to unmountif (!parcelError) {appOrParcel.status = NOT_MOUNTED;}}).catch((err) => {if (hardFail) {throw transformErr(err, appOrParcel, SKIP_BECAUSE_BROKEN);} else {handleAppError(err, appOrParcel, SKIP_BECAUSE_BROKEN);}});}});
}

tryToBootstrapAndMount

single-spa/src/navigation/reroute.js

/*** Let's imagine that some kind of delay occurred during application loading.* The user without waiting for the application to load switched to another route,* this means that we shouldn't bootstrap and mount that application, thus we check* twice if that application should be active before bootstrapping and mounting.* https://github.com/single-spa/single-spa/issues/524* 这里这个两次判断还是很重要的*/
function tryToBootstrapAndMount(app, unmountAllPromise) {if (shouldBeActive(app)) {// 一次判断为true，才会执行初始化return toBootstrapPromise(app).then((app) =>unmountAllPromise.then(() =>// 第二次, 两次都为true才会去挂载shouldBeActive(app) ? toMountPromise(app) : app));} else {// 卸载return unmountAllPromise.then(() => app);}
}

toBootstrapPromise

single-spa/src/lifecycles/bootstrap.js

// 初始化app，更改app.status，在合理的时间内执行bootstrap生命周期函数
export function toBootstrapPromise(appOrParcel, hardFail) {return Promise.resolve().then(() => {if (appOrParcel.status !== NOT_BOOTSTRAPPED) {return appOrParcel;}appOrParcel.status = BOOTSTRAPPING;return reasonableTime(appOrParcel, "bootstrap").then(() => {appOrParcel.status = NOT_MOUNTED;return appOrParcel;}).catch((err) => {if (hardFail) {throw transformErr(err, appOrParcel, SKIP_BECAUSE_BROKEN);} else {handleAppError(err, appOrParcel, SKIP_BECAUSE_BROKEN);return appOrParcel;}});});
}

toMountPromise

single-spa/src/lifecycles/mount.js

// 挂载app，执行mount生命周期函数，并更改app.status
export function toMountPromise(appOrParcel, hardFail) {return Promise.resolve().then(() => {if (appOrParcel.status !== NOT_MOUNTED) {return appOrParcel;}if (!beforeFirstMountFired) {window.dispatchEvent(new CustomEvent("single-spa:before-first-mount"));beforeFirstMountFired = true;}return reasonableTime(appOrParcel, "mount").then(() => {appOrParcel.status = MOUNTED;if (!firstMountFired) {// single-spa其实在不同的阶段提供了相应的自定义事件，让用户可以做一些事情window.dispatchEvent(new CustomEvent("single-spa:first-mount"));firstMountFired = true;}return appOrParcel;}).catch((err) => {// If we fail to mount the appOrParcel, we should attempt to unmount it before putting in SKIP_BECAUSE_BROKEN// We temporarily put the appOrParcel into MOUNTED status so that toUnmountPromise actually attempts to unmount it// instead of just doing a no-op.appOrParcel.status = MOUNTED;return toUnmountPromise(appOrParcel, true).then(setSkipBecauseBroken,setSkipBecauseBroken);function setSkipBecauseBroken() {if (!hardFail) {handleAppError(err, appOrParcel, SKIP_BECAUSE_BROKEN);return appOrParcel;} else {throw transformErr(err, appOrParcel, SKIP_BECAUSE_BROKEN);}}});});
}

start(opts)

single-spa/src/start.js

let started = false
/*** https://zh-hans.single-spa.js.org/docs/api#start* 调用start之前，应用会被加载，但不会初始化、挂载和卸载，有了start可以更好的控制应用的性能* @param {*} opts */
export function start(opts) {started = true;if (opts && opts.urlRerouteOnly) {setUrlRerouteOnly(opts.urlRerouteOnly);}if (isInBrowser) {reroute();}
}export function isStarted() {return started;
}if (isInBrowser) {// registerApplication之后如果一直没有调用start，则在5000ms后给出警告提示setTimeout(() => {if (!started) {console.warn(formatErrorMessage(1,__DEV__ &&`singleSpa.start() has not been called, 5000ms after single-spa was loaded. Before start() is called, apps can be declared and loaded, but not bootstrapped or mounted.`));}}, 5000);
}

监听路由变化

single-spa/src/navigation/navigation-events.js

以下代码会被打包进bundle的全局作用域内，bundle被加载以后就会自动执行。这句提示不需要的话可自动忽略

/*** 监听路由变化*/
if (isInBrowser) {// We will trigger an app change for any routing events，监听hashchange和popstate事件window.addEventListener("hashchange", urlReroute);window.addEventListener("popstate", urlReroute);// Monkeypatch addEventListener so that we can ensure correct timing/*** 扩展原生的addEventListener和removeEventListener方法* 每次注册事件和事件处理函数都会将事件和处理函数保存下来，当然移除时也会做删除* */ const originalAddEventListener = window.addEventListener;const originalRemoveEventListener = window.removeEventListener;window.addEventListener = function (eventName, fn) {if (typeof fn === "function") {if (// eventName只能是hashchange或popstate && 对应事件的fn注册函数没有注册routingEventsListeningTo.indexOf(eventName) >= 0 &&!find(capturedEventListeners[eventName], (listener) => listener === fn)) {// 注册（保存）eventName 事件的处理函数capturedEventListeners[eventName].push(fn);return;}}// 原生方法return originalAddEventListener.apply(this, arguments);};window.removeEventListener = function (eventName, listenerFn) {if (typeof listenerFn === "function") {// 从captureEventListeners数组中移除eventName事件指定的事件处理函数if (routingEventsListeningTo.indexOf(eventName) >= 0) {capturedEventListeners[eventName] = capturedEventListeners[eventName].filter((fn) => fn !== listenerFn);return;}}return originalRemoveEventListener.apply(this, arguments);};// 增强pushstate和replacestatewindow.history.pushState = patchedUpdateState(window.history.pushState,"pushState");window.history.replaceState = patchedUpdateState(window.history.replaceState,"replaceState");if (window.singleSpaNavigate) {console.warn(formatErrorMessage(41,__DEV__ &&"single-spa has been loaded twice on the page. This can result in unexpected behavior."));} else {/* For convenience in `onclick` attributes, we expose a global function for navigating to* whatever an <a> tag's href is.* singleSpa暴露出来的一个全局方法，用户也可以基于它去判断子应用是运行在基座应用上还是独立运行*/window.singleSpaNavigate = navigateToUrl;}
}

patchedUpdateState

single-spa/src/navigation/navigation-events.js

/*** 通过装饰器模式，增强pushstate和replacestate方法，除了原生的操作历史记录，还会调用reroute* @param {*} updateState window.history.pushstate/replacestate* @param {*} methodName 'pushstate' or 'replacestate'*/
function patchedUpdateState(updateState, methodName) {return function () {// 当前urlconst urlBefore = window.location.href;// pushstate或者replacestate的执行结果const result = updateState.apply(this, arguments);// pushstate或replacestate执行后的url地址const urlAfter = window.location.href;// 如果调用start传递了参数urlRerouteOnly为true，则这里不会触发reroute// https://zh-hans.single-spa.js.org/docs/api#startif (!urlRerouteOnly || urlBefore !== urlAfter) {urlReroute(createPopStateEvent(window.history.state, methodName));}return result;};
}

createPopStateEvent

single-spa/src/navigation/navigation-events.js

function createPopStateEvent(state, originalMethodName) {// https://github.com/single-spa/single-spa/issues/224 and https://github.com/single-spa/single-spa-angular/issues/49// We need a popstate event even though the browser doesn't do one by default when you call replaceState, so that// all the applications can reroute. We explicitly identify this extraneous event by setting singleSpa=true and// singleSpaTrigger=<pushState|replaceState> on the event instance.let evt;try {evt = new PopStateEvent("popstate", { state });} catch (err) {// IE 11 compatibility https://github.com/single-spa/single-spa/issues/299// https://docs.microsoft.com/en-us/openspecs/ie_standards/ms-html5e/bd560f47-b349-4d2c-baa8-f1560fb489ddevt = document.createEvent("PopStateEvent");evt.initPopStateEvent("popstate", false, false, state);}evt.singleSpa = true;evt.singleSpaTrigger = originalMethodName;return evt;
}

urlReroute

single-spa/src/navigation/navigation-events.js

export function setUrlRerouteOnly(val) {urlRerouteOnly = val;
}function urlReroute() {reroute([], arguments);
}

小结

以上就是对整个single-spa框架源码的解读，相信读到这里你会有不一样的理解吧，当然第一遍读完你有可能有点懵，我当时就是这样，这时候就需要那句古话了，书读百遍，其义自现（干了这碗鸡汤）

整个框架的源码读完以后，你会发现：single-spa的原理其实很简单，它就是一个子应用加载器 + 状态机的结合体，而且具体怎么加载子应用还是基座应用提供的；框架里面维护了各个子应用的状态，以及在适当的时候负责更改子应用的状态、执行相应的生命周期函数

想想框架好像也不复杂，对吧？？那接下来就来实现一个自己的single-spa框架吧

手写 single-spa 框架

经过上面的阅读，相信对single-spa已经有一定的理解了，接下来就来实现一个自己的single-spa，就叫lyn-single-spa吧。

我们好像只需要实现registerApplication和start两个方法并导出即可。

写代码之前，必须理清框架内子应用的各个状态以及状态的变更过程，为了便于理解，代码写详细的注释，希望大家看完以后都可以实现一个自己的single-spa

// 实现子应用的注册、挂载、切换、卸载功能/*** 子应用状态*/
// 子应用注册以后的初始状态
const NOT_LOADED = 'NOT_LOADED'
// 表示正在加载子应用源代码
const LOADING_SOURCE_CODE = 'LOADING_SOURCE_CODE'
// 执行完 app.loadApp，即子应用加载完以后的状态
const NOT_BOOTSTRAPPED = 'NOT_BOOTSTRAPPED'
// 正在初始化
const BOOTSTRAPPING = 'BOOTSTRAPPING'
// 执行 app.bootstrap 之后的状态，表是初始化完成，处于未挂载的状态
const NOT_MOUNTED = 'NOT_MOUNTED'
// 正在挂载
const MOUNTING = 'MOUNTING'
// 挂载完成，app.mount 执行完毕
const MOUNTED = 'MOUNTED'
const UPDATING = 'UPDATING'
// 正在卸载
const UNMOUNTING = 'UNMOUNTING'
// 以下三种状态这里没有涉及
const UNLOADING = 'UNLOADING'
const LOAD_ERROR = 'LOAD_ERROR'
const SKIP_BECAUSE_BROKEN = 'SKIP_BECAUSE_BROKEN'// 存放所有的子应用
const apps = []/*** 注册子应用* @param {*} appConfig = {*    name: '',*    app: promise function,*    activeWhen: location => location.pathname.startsWith(path),*    customProps: {}* }*/
export function registerApplication (appConfig) {apps.push(Object.assign({}, appConfig, { status: NOT_LOADED }))reroute()
}// 启动
let isStarted = false
export function start () {isStarted = true
}function reroute () {// 三类 appconst { appsToLoad, appsToMount, appsToUnmount } = getAppChanges()if (isStarted) {performAppChanges()} else {loadApps()}function loadApps () {appsToLoad.map(toLoad)}function performAppChanges () {// 卸载appsToUnmount.map(toUnmount)// 初始化 + 挂载appsToMount.map(tryToBoostrapAndMount)}
}/*** 挂载应用* @param {*} app */
async function tryToBoostrapAndMount(app) {if (shouldBeActive(app)) {// 正在初始化app.status = BOOTSTRAPPING// 初始化await app.bootstrap// 初始化完成app.status = NOT_MOUNTED// 第二次判断是为了防止中途用户切换路由if (shouldBeActive(app)) {// 正在挂载app.status = MOUNTING// 挂载await app.mount()// 挂载完成app.status = MOUNTED}}
}/*** 卸载应用* @param {*} app */
async function toUnmount (app) {if (app.status !== 'MOUNTED') return app// 更新状态为正在卸载app.status = MOUNTING// 执行卸载await app.unmount()// 卸载完成app.status = NOT_MOUNTEDreturn app
}/*** 加载子应用* @param {*} app */
async function toLoad (app) {if (app.status !== NOT_LOADED) return app// 更改状态为正在加载app.status = LOADING_SOURCE_CODE// 加载 appconst res = await app.app()// 加载完成app.status = NOT_BOOTSTRAPPED// 将子应用导出的生命周期函数挂载到 app 对象上app.bootstrap = res.bootstrapapp.mount = res.mountapp.unmount = res.unmountapp.unload = res.unload// 加载完以后执行 reroute 尝试挂载reroute()return app
}/*** 将所有的子应用分为三大类，待加载、待挂载、待卸载*/
function getAppChanges () {const appsToLoad = [],appsToMount = [],appsToUnmount = []apps.forEach(app => {switch (app.status) {// 待加载case NOT_LOADED:appsToLoad.push(app)break// 初始化 + 挂载case NOT_BOOTSTRAPPED:case NOT_MOUNTED:if (shouldBeActive(app)) {appsToMount.push(app)} break// 待卸载case MOUNTED:if (!shouldBeActive(app)) {appsToUnmount.push(app)}break}})return { appsToLoad, appsToMount, appsToUnmount }
}/*** 应用需要激活吗 ？* @param {*} app * return true or false*/
function shouldBeActive (app) {try {return app.activeWhen(window.location)} catch (err) {console.error('shouldBeActive function error', err);return false}
}// 让子应用判断自己是否运行在基座应用中
window.singleSpaNavigate = true
// 监听路由
window.addEventListener('hashchange', reroute)
window.history.pushState = patchedUpdateState(window.history.pushState)
window.history.replaceState = patchedUpdateState(window.history.replaceState)
/*** 装饰器，增强 pushState 和 replaceState 方法* @param {*} updateState */
function patchedUpdateState (updateState) {return function (...args) {// 当前urlconst urlBefore = window.location.href;// pushState or replaceState 的执行结果const result = Reflect.apply(updateState, this, args)// 执行updateState之后的urlconst urlAfter = window.location.hrefif (urlBefore !== urlAfter) {reroute()}return result}
}

看着是不是很简单，加注释也才200行而已，当然，这只是一个简版的single-spa框架，没什么健壮性可言，但也正因为简单，所以更能说明single-spa框架的本质。

single-spa-vue 源码分析

single-spa-vue负责为vue应用生成通用的生命周期钩子，这些钩子函数负责子应用的初始化、挂载、更新（数据）、卸载。

import "css.escape";const defaultOpts = {// required optsVue: null,appOptions: null,template: null
};/*** 判断参数的合法性* 返回生命周期函数，其中的mount方法负责实例化子应用，update方法提供了基座应用和子应用通信的机会，unmount卸载子应用，bootstrap感觉没啥用* @param {*} userOpts = {*    Vue,*    appOptions: {*      el: '#id',*      store,*      router,*      render: h => h(App)*    } * }* return 四个生命周期函数组成的对象*/
export default function singleSpaVue(userOpts) {// objectif (typeof userOpts !== "object") {throw new Error(`single-spa-vue requires a configuration object`);}// 合并用户选项和默认选项const opts = {...defaultOpts,...userOpts};// Vue构造函数if (!opts.Vue) {throw Error("single-spa-vue must be passed opts.Vue");}// appOptionsif (!opts.appOptions) {throw Error("single-spa-vue must be passed opts.appOptions");}// el选择器if (opts.appOptions.el &&typeof opts.appOptions.el !== "string" &&!(opts.appOptions.el instanceof HTMLElement)) {throw Error(`single-spa-vue: appOptions.el must be a string CSS selector, an HTMLElement, or not provided at all. Was given ${typeof opts.appOptions.el}`);}// Just a shared object to store the mounted object state// key - name of single-spa app, since it is uniquelet mountedInstances = {};/*** 返回一个对象，每个属性都是一个生命周期函数*/return {bootstrap: bootstrap.bind(null, opts, mountedInstances),mount: mount.bind(null, opts, mountedInstances),unmount: unmount.bind(null, opts, mountedInstances),update: update.bind(null, opts, mountedInstances)};
}function bootstrap(opts) {if (opts.loadRootComponent) {return opts.loadRootComponent().then(root => (opts.rootComponent = root));} else {return Promise.resolve();}
}/*** 做了三件事情：*  大篇幅的处理el元素*  然后是render函数*  实例化子应用*/
function mount(opts, mountedInstances, props) {const instance = {};return Promise.resolve().then(() => {const appOptions = { ...opts.appOptions };// 可以通过props.domElement属性单独设置自应用的渲染DOM容器，当然appOptions.el必须为空if (props.domElement && !appOptions.el) {appOptions.el = props.domElement;}let domEl;if (appOptions.el) {if (typeof appOptions.el === "string") {// 子应用的DOM容器domEl = document.querySelector(appOptions.el);if (!domEl) {throw Error(`If appOptions.el is provided to single-spa-vue, the dom element must exist in the dom. Was provided as ${appOptions.el}`);}} else {// 处理DOM容器是元素的情况domEl = appOptions.el;if (!domEl.id) {// 设置元素IDdomEl.id = `single-spa-application:${props.name}`;}appOptions.el = `#${CSS.escape(domEl.id)}`;}} else {// 当然如果没有id，这里会自动生成一个idconst htmlId = `single-spa-application:${props.name}`;appOptions.el = `#${CSS.escape(htmlId)}`;domEl = document.getElementById(htmlId);if (!domEl) {domEl = document.createElement("div");domEl.id = htmlId;document.body.appendChild(domEl);}}appOptions.el = appOptions.el + " .single-spa-container";// single-spa-vue@>=2 always REPLACES the `el` instead of appending to it.// We want domEl to stick around and not be replaced. So we tell Vue to mount// into a container div inside of the main domElif (!domEl.querySelector(".single-spa-container")) {const singleSpaContainer = document.createElement("div");singleSpaContainer.className = "single-spa-container";domEl.appendChild(singleSpaContainer);}instance.domEl = domEl;// renderif (!appOptions.render && !appOptions.template && opts.rootComponent) {appOptions.render = h => h(opts.rootComponent);}// dataif (!appOptions.data) {appOptions.data = {};}appOptions.data = { ...appOptions.data, ...props };// 实例化子应用instance.vueInstance = new opts.Vue(appOptions);if (instance.vueInstance.bind) {instance.vueInstance = instance.vueInstance.bind(instance.vueInstance);}mountedInstances[props.name] = instance;return instance.vueInstance;});
}// 基座应用通过update生命周期函数可以更新子应用的属性
function update(opts, mountedInstances, props) {return Promise.resolve().then(() => {// 应用实例const instance = mountedInstances[props.name];// 所有的属性const data = {...(opts.appOptions.data || {}),...props};// 更新实例对象上的属性值，vm.test = 'xxx'for (let prop in data) {instance.vueInstance[prop] = data[prop];}});
}// 调用$destroy钩子函数，销毁子应用
function unmount(opts, mountedInstances, props) {return Promise.resolve().then(() => {const instance = mountedInstances[props.name];instance.vueInstance.$destroy();instance.vueInstance.$el.innerHTML = "";delete instance.vueInstance;if (instance.domEl) {instance.domEl.innerHTML = "";delete instance.domEl;}});
}

结语

到这里就结束了，文章比较长，写这篇文章也花费了好几天的时间，但是感觉真的很好，收获满满，特别是最后手写框架部分。

也给各位同学一个建议，一定要勤动手，不动笔墨不读书，当你真的把框架写出来时，那个感觉是只看源码完全所不能比拟的，检验你是否真的懂框架原理的最好办法，就是看你能否写一个框架出来。

愿同学们也能收获满满！！

共同学习，共同进步～～

github: https://github.com/liyongning/micro-frontend.git

❤️爱心三连击1.看到这里了就点个在看支持下吧，你的「在看」是我创作的动力。
2.关注公众号程序员成长指北，回复「1」加入Node进阶交流群！「在这里有好多 Node 开发者，会讨论 Node 知识，互相学习」！
3.也可添加微信【ikoala520】，一起成长。“在看转发”是最大的支持