Vue路由History模式分析

Vue-router是Vue的核心组件，主要是作为Vue的路由管理器，Vue-router默认hash模式，通过引入Vue-router对象模块时配置mode属性可以启用history模式。

描述

Vue-router的hash模式使用URL的Hash来模拟一个完整的URL，当URL改变时页面不会重新加载，而Vue-router的history模式是充分利用history.pushState的API来完成URL跳转，同样在页面跳转时无须重新加载页面，当然也不会对于服务端进行请求，当然对于history模式仍然是需要后端的配置支持，由于应用是个单页客户端应用，如果后台没有正确的配置，当用户在浏览器直接访问URL时就会返回404，所以需要在服务端增加一个覆盖所有情况的候选资源，如果URL匹配不到任何静态资源时，则应该返回同一个index.html应用依赖页面，例如在Nginx下的配置。

location / {
  try_files $uri $uri/ /index.html;
}

分析

Vue-router源码的实现比较复杂，会处理各种兼容问题与异常以及各种条件分支，文章分析比较核心的代码部分，精简过后的版本，重要部分做出注释，commit id为560d11d。

首先是在定义Router时调用Vue.use(VueRouter)，这是Vue.js插件的经典写法，给插件对象增加install方法用来安装插件具体逻辑，此时会调用VueRouter类上的静态方法，即VueRouter.install = install，install模块主要是保证Vue-router只被use一次，以及通过mixin在Vue的生命周期beforeCreate内注册实例，在destroyed内销毁实例，还有定义$router与$route属性为只读属性以及<router-view>与<router-link>全局组件的注册。

// dev/src/install.js line 6
export function install (Vue) {
  if (install.installed && _Vue === Vue) return
  install.installed = true // 保证 Vue-router 只被 use 一次

  _Vue = Vue

  const isDef = v => v !== undefined

  const registerInstance = (vm, callVal) => {
    let i = vm.$options._parentVnode
    if (isDef(i) && isDef(i = i.data) && isDef(i = i.registerRouteInstance)) {
      i(vm, callVal)
    }
  }

  Vue.mixin({
    beforeCreate () { // 注册实例
      if (isDef(this.$options.router)) { // this.$options.router 来自于 VueRouter 的实例化 // 判断实例是否已经挂载
        this._routerRoot = this
        this._router = this.$options.router
        this._router.init(this) // // 调用 VueRouter 的 init 方法 // 后文会说明 init 方法的作用
        Vue.util.defineReactive(this, '_route', this._router.history.current)
      } else {
        this._routerRoot = (this.$parent && this.$parent._routerRoot) || this // 将组件的 _routerRoot 都指向根 Vue 实例
      }
      registerInstance(this, this)
    },
    destroyed () { // 销毁实例 即挂载undefined
      registerInstance(this)
    }
  })

  Object.defineProperty(Vue.prototype, '$router', {
    get () { return this._routerRoot._router }
  })

  Object.defineProperty(Vue.prototype, '$route', {
    get () { return this._routerRoot._route }
  })

  Vue.component('RouterView', View) // 注册全局组件 <router-view>
  Vue.component('RouterLink', Link) // 注册全局组件 <router-link>

  const strats = Vue.config.optionMergeStrategies
  // use the same hook merging strategy for route hooks
  strats.beforeRouteEnter = strats.beforeRouteLeave = strats.beforeRouteUpdate = strats.created
}

之后是VueRouter对象的构造函数，主要是先获取mode的值，如果mode的值为history但是浏览器不支持history模式,那么就强制设置mode值为hash，接下来根据mode的值，来选择vue-router使用哪种模式。

// dev/src/index.js line 40
constructor (options: RouterOptions = {}) {
  this.app = null
  this.apps = []
  this.options = options
  this.beforeHooks = []
  this.resolveHooks = []
  this.afterHooks = []
  this.matcher = createMatcher(options.routes || [], this) // 创建路由匹配对象

  let mode = options.mode || 'hash'
  this.fallback =
    mode === 'history' && !supportsPushState && options.fallback !== false // 检车兼容
  if (this.fallback) {
    mode = 'hash'
  }
  if (!inBrowser) {
    mode = 'abstract'
  }
  this.mode = mode

  switch (mode) {
    case 'history':
      this.history = new HTML5History(this, options.base) // 实例化history模式
      break
    case 'hash':
      this.history = new HashHistory(this, options.base, this.fallback) // 实例化Hash模式
      break
    case 'abstract':
      this.history = new AbstractHistory(this, options.base)
      break
    default:
      if (process.env.NODE_ENV !== 'production') {
        assert(false, `invalid mode: ${mode}`)
      }
  }
}

在构造函数中调用了创建路由匹配对象的方法createMatcher，而在createMatcher中又调用了实际用以创建路由映射表的方法createRouteMap，可以说createMatcher函数的作用就是创建路由映射表，然后通过闭包的方式让addRoutes和match函数能够使用路由映射表的几个对象，最后返回一个Matcher对象。

// dev/src/create-matcher.js line 16
export function createMatcher (
  routes: Array<RouteConfig>,
  router: VueRouter
): Matcher {
  const { pathList, pathMap, nameMap } = createRouteMap(routes) // 创建路由映射表

  function addRoutes (routes) {
    createRouteMap(routes, pathList, pathMap, nameMap)
  }

  function match ( // 路由匹配
    raw: RawLocation,
    currentRoute?: Route,
    redirectedFrom?: Location
  ): Route {
    const location = normalizeLocation(raw, currentRoute, false, router) // location 是一个对象，类似于 {"_normalized":true,"path":"/","query":{},"hash":""}
    const { name } = location

    if (name) { // 如果有路由名称 就进行nameMap映射
      const record = nameMap[name]  // nameMap[name] = 路由记录
      if (process.env.NODE_ENV !== 'production') {
        warn(record, `Route with name '${name}' does not exist`)
      }
      if (!record) return _createRoute(null, location)
      const paramNames = record.regex.keys
        .filter(key => !key.optional)
        .map(key => key.name)

      if (typeof location.params !== 'object') {
        location.params = {}
      }

      if (currentRoute && typeof currentRoute.params === 'object') {
        for (const key in currentRoute.params) {
          if (!(key in location.params) && paramNames.indexOf(key) > -1) {
            location.params[key] = currentRoute.params[key]
          }
        }
      }

      location.path = fillParams(record.path, location.params, `named route "${name}"`)
      return _createRoute(record, location, redirectedFrom)
    } else if (location.path) { // 如果路由配置了path，到pathList和PathMap里匹配到路由记录 
      location.params = {}
      for (let i = 0; i < pathList.length; i++) {
        const path = pathList[i]
        const record = pathMap[path]
        if (matchRoute(record.regex, location.path, location.params)) {
          return _createRoute(record, location, redirectedFrom)
        }
      }
    }
    // no match
    return _createRoute(null, location)
  }

  function redirect ( // 处理重定向
    record: RouteRecord,
    location: Location
  ): Route {
    const originalRedirect = record.redirect
    let redirect = typeof originalRedirect === 'function'
      ? originalRedirect(createRoute(record, location, null, router))
      : originalRedirect

    if (typeof redirect === 'string') {
      redirect = { path: redirect }
    }

    if (!redirect || typeof redirect !== 'object') {
      if (process.env.NODE_ENV !== 'production') {
        warn(
          false, `invalid redirect option: ${JSON.stringify(redirect)}`
        )
      }
      return _createRoute(null, location)
    }

    const re: Object = redirect
    const { name, path } = re
    let { query, hash, params } = location
    query = re.hasOwnProperty('query') ? re.query : query
    hash = re.hasOwnProperty('hash') ? re.hash : hash
    params = re.hasOwnProperty('params') ? re.params : params

    if (name) {
      // resolved named direct
      const targetRecord = nameMap[name]
      if (process.env.NODE_ENV !== 'production') {
        assert(targetRecord, `redirect failed: named route "${name}" not found.`)
      }
      return match({
        _normalized: true,
        name,
        query,
        hash,
        params
      }, undefined, location)
    } else if (path) {
      // 1. resolve relative redirect
      const rawPath = resolveRecordPath(path, record)
      // 2. resolve params
      const resolvedPath = fillParams(rawPath, params, `redirect route with path "${rawPath}"`)
      // 3. rematch with existing query and hash
      return match({
        _normalized: true,
        path: resolvedPath,
        query,
        hash
      }, undefined, location)
    } else {
      if (process.env.NODE_ENV !== 'production') {
        warn(false, `invalid redirect option: ${JSON.stringify(redirect)}`)
      }
      return _createRoute(null, location)
    }
  }

  function alias ( // 处理别名
    record: RouteRecord,
    location: Location,
    matchAs: string
  ): Route {
    const aliasedPath = fillParams(matchAs, location.params, `aliased route with path "${matchAs}"`)
    const aliasedMatch = match({
      _normalized: true,
      path: aliasedPath
    })
    if (aliasedMatch) {
      const matched = aliasedMatch.matched
      const aliasedRecord = matched[matched.length - 1]
      location.params = aliasedMatch.params
      return _createRoute(aliasedRecord, location)
    }
    return _createRoute(null, location)
  }

  function _createRoute (  // 创建路由
    record: ?RouteRecord,
    location: Location,
    redirectedFrom?: Location
  ): Route {
    if (record && record.redirect) {
      return redirect(record, redirectedFrom || location)
    }
    if (record && record.matchAs) {
      return alias(record, location, record.matchAs)
    }
    return createRoute(record, location, redirectedFrom, router) // 创建路由对象
  }

  return {
    match,
    addRoutes
  }
}

// dev/src/create-route-map.js line 7
export function createRouteMap (
  routes: Array<RouteConfig>,
  oldPathList?: Array<string>,
  oldPathMap?: Dictionary<RouteRecord>,
  oldNameMap?: Dictionary<RouteRecord>
): {
  pathList: Array<string>,
  pathMap: Dictionary<RouteRecord>,
  nameMap: Dictionary<RouteRecord>
} {
  // the path list is used to control path matching priority
  const pathList: Array<string> = oldPathList || [] // 创建映射表
  // $flow-disable-line
  const pathMap: Dictionary<RouteRecord> = oldPathMap || Object.create(null)
  // $flow-disable-line
  const nameMap: Dictionary<RouteRecord> = oldNameMap || Object.create(null)

  routes.forEach(route => { // 遍历路由配置，为每个配置添加路由记录
    addRouteRecord(pathList, pathMap, nameMap, route)
  })

  // ensure wildcard routes are always at the end
  for (let i = 0, l = pathList.length; i < l; i++) { // 确保通配符在最后
    if (pathList[i] === '*') {
      pathList.push(pathList.splice(i, 1)[0])
      l--
      i--
    }
  }

  if (process.env.NODE_ENV === 'development') {
    // warn if routes do not include leading slashes
    const found = pathList
    // check for missing leading slash
      .filter(path => path && path.charAt(0) !== '*' && path.charAt(0) !== '/')

    if (found.length > 0) {
      const pathNames = found.map(path => `- ${path}`).join('\n')
      warn(false, `Non-nested routes must include a leading slash character. Fix the following routes: \n${pathNames}`)
    }
  }

  return {
    pathList,
    pathMap,
    nameMap
  }
}

function addRouteRecord ( // 添加路由记录
  pathList: Array<string>,
  pathMap: Dictionary<RouteRecord>,
  nameMap: Dictionary<RouteRecord>,
  route: RouteConfig,
  parent?: RouteRecord,
  matchAs?: string
) {
  const { path, name } = route // 获得路由配置下的属性
  if (process.env.NODE_ENV !== 'production') {
    assert(path != null, `"path" is required in a route configuration.`)
    assert(
      typeof route.component !== 'string',
      `route config "component" for path: ${String(
        path || name
      )} cannot be a ` + `string id. Use an actual component instead.`
    )
  }

  const pathToRegexpOptions: PathToRegexpOptions =
    route.pathToRegexpOptions || {}
  const normalizedPath = normalizePath(path, parent, pathToRegexpOptions.strict)

  if (typeof route.caseSensitive === 'boolean') {
    pathToRegexpOptions.sensitive = route.caseSensitive
  }

  const record: RouteRecord = { // 生成记录对象
    path: normalizedPath,
    regex: compileRouteRegex(normalizedPath, pathToRegexpOptions),
    components: route.components || { default: route.component },
    instances: {},
    name,
    parent,
    matchAs,
    redirect: route.redirect,
    beforeEnter: route.beforeEnter,
    meta: route.meta || {},
    props:
      route.props == null
        ? {}
        : route.components
          ? route.props
          : { default: route.props }
  }

  if (route.children) { 
    // Warn if route is named, does not redirect and has a default child route.
    // If users navigate to this route by name, the default child will
    // not be rendered (GH Issue #629)
    if (process.env.NODE_ENV !== 'production') {
      if (
        route.name &&
        !route.redirect &&
        route.children.some(child => /^\/?$/.test(child.path))
      ) {
        warn(
          false,
          `Named Route '${route.name}' has a default child route. ` +
            `When navigating to this named route (:to="{name: '${
              route.name
            }'"), ` +
            `the default child route will not be rendered. Remove the name from ` +
            `this route and use the name of the default child route for named ` +
            `links instead.`
        )
      }
    }
    route.children.forEach(child => { // 递归路由配置的 children 属性，添加路由记录
      const childMatchAs = matchAs
        ? cleanPath(`${matchAs}/${child.path}`)
        : undefined
      addRouteRecord(pathList, pathMap, nameMap, child, record, childMatchAs)
    })
  }

  if (!pathMap[record.path]) { // 如果有多个相同的路径，只有第一个起作用，后面的会被忽略
    pathList.push(record.path)
    pathMap[record.path] = record
  }

  if (route.alias !== undefined) { // 如果路由有别名的话，给别名也添加路由记录
    const aliases = Array.isArray(route.alias) ? route.alias : [route.alias]
    for (let i = 0; i < aliases.length; ++i) {
      const alias = aliases[i]
      if (process.env.NODE_ENV !== 'production' && alias === path) {
        warn(
          false,
          `Found an alias with the same value as the path: "${path}". You have to remove that alias. It will be ignored in development.`
        )
        // skip in dev to make it work
        continue
      }

      const aliasRoute = {
        path: alias,
        children: route.children
      }
      addRouteRecord(
        pathList,
        pathMap,
        nameMap,
        aliasRoute,
        parent,
        record.path || '/' // matchAs
      )
    }
  }

  if (name) {
    if (!nameMap[name]) {
      nameMap[name] = record
    } else if (process.env.NODE_ENV !== 'production' && !matchAs) {
      warn(
        false,
        `Duplicate named routes definition: ` +
          `{ name: "${name}", path: "${record.path}" }`
      )
    }
  }
}

在上文的构造函数中实例化的HTML5History对象就是对于history模式下的路由的处理，主要是通过继承History对象以及自身实现的方法完成路由。在初始化VueRouter时调用的init方法调用了路由切换以及调用了setupListeners方法实现了路由的切换的监听回调，注意此时并没有在HTML5History对象的构造函数中直接添加事件监听，这是因为需要避免在某些浏览器中调度第一个popstate事件，但是由于异步保护，第一个历史记录路由未同时更新的问题。history模式的代码结构以及更新视图的逻辑与hash模式基本类似，主要是监听popstate事件以及对于push()和replace()方法的变动，使用History对象的pushState()与replaceState()等方法进行路由的变换。

// dev/src/index.js line 21
export default class VueRouter {
  //...
  init (app: any /* Vue component instance */) {
    process.env.NODE_ENV !== 'production' &&
      assert(
        install.installed,
        `not installed. Make sure to call \`Vue.use(VueRouter)\` ` +
          `before creating root instance.`
      )

    this.apps.push(app)

    // set up app destroyed handler
    // https://github.com/vuejs/vue-router/issues/2639
    app.$once('hook:destroyed', () => {
      // clean out app from this.apps array once destroyed
      const index = this.apps.indexOf(app)
      if (index > -1) this.apps.splice(index, 1)
      // ensure we still have a main app or null if no apps
      // we do not release the router so it can be reused
      if (this.app === app) this.app = this.apps[0] || null

      if (!this.app) this.history.teardown()
    })

    // main app previously initialized
    // return as we don't need to set up new history listener
    if (this.app) {
      return
    }

    this.app = app

    const history = this.history

    if (history instanceof HTML5History || history instanceof HashHistory) {
      const handleInitialScroll = routeOrError => {
        const from = history.current
        const expectScroll = this.options.scrollBehavior
        const supportsScroll = supportsPushState && expectScroll

        if (supportsScroll && 'fullPath' in routeOrError) {
          handleScroll(this, routeOrError, from, false)
        }
      }
      const setupListeners = routeOrError => {
        history.setupListeners() // 初始化添加事件监听
        handleInitialScroll(routeOrError)
      }
      history.transitionTo( // 如果默认页，需要根据当前浏览器地址栏里的 path 或者 hash 来激活对应的路由
        history.getCurrentLocation(),
        setupListeners,
        setupListeners
      )
    }

    history.listen(route => {
      this.apps.forEach(app => {
        app._route = route
      })
    })
  }
  //...
}

// dev/src/history/base.js line 24
export class History {
  // ...

  transitionTo (
    location: RawLocation,
    onComplete?: Function,
    onAbort?: Function
  ) {
    let route
    // catch redirect option https://github.com/vuejs/vue-router/issues/3201
    try {
      route = this.router.match(location, this.current) // // 获取匹配的路由信息
    } catch (e) {
      this.errorCbs.forEach(cb => {
        cb(e)
      })
      // Exception should still be thrown
      throw e
    }
    const prev = this.current
    this.confirmTransition( // 确认跳转
      route,
      () => {
        this.updateRoute(route) // 更新当前 route 对象
        onComplete && onComplete(route)
        this.ensureURL() // 子类实现的更新url地址 对于 hash 模式的话 就是更新 hash 的值
        this.router.afterHooks.forEach(hook => {
          hook && hook(route, prev)
        })

        // fire ready cbs once
        if (!this.ready) {
          this.ready = true
          this.readyCbs.forEach(cb => {
            cb(route)
          })
        }
      },
      err => {
        if (onAbort) {
          onAbort(err)
        }
        if (err && !this.ready) {
          // Initial redirection should not mark the history as ready yet
          // because it's triggered by the redirection instead
          // https://github.com/vuejs/vue-router/issues/3225
          // https://github.com/vuejs/vue-router/issues/3331
          if (!isNavigationFailure(err, NavigationFailureType.redirected) || prev !== START) {
            this.ready = true
            this.readyErrorCbs.forEach(cb => {
              cb(err)
            })
          }
        }
      }
    )
  }

  confirmTransition (route: Route, onComplete: Function, onAbort?: Function) {
    const current = this.current
    this.pending = route
    const abort = err => {
      // changed after adding errors with
      // https://github.com/vuejs/vue-router/pull/3047 before that change,
      // redirect and aborted navigation would produce an err == null
      if (!isNavigationFailure(err) && isError(err)) {
        if (this.errorCbs.length) {
          this.errorCbs.forEach(cb => {
            cb(err)
          })
        } else {
          warn(false, 'uncaught error during route navigation:')
          console.error(err)
        }
      }
      onAbort && onAbort(err)
    }
    const lastRouteIndex = route.matched.length - 1
    const lastCurrentIndex = current.matched.length - 1
    if (
      isSameRoute(route, current) && // 如果是相同的路由就不跳转
      // in the case the route map has been dynamically appended to
      lastRouteIndex === lastCurrentIndex &&
      route.matched[lastRouteIndex] === current.matched[lastCurrentIndex]
    ) {
      this.ensureURL()
      return abort(createNavigationDuplicatedError(current, route))
    }

    const { updated, deactivated, activated } = resolveQueue( // 通过对比路由解析出可复用的组件，需要渲染的组件，失活的组件
      this.current.matched,
      route.matched
    )

    const queue: Array<?NavigationGuard> = [].concat( // 导航守卫数组
      // in-component leave guards
      extractLeaveGuards(deactivated),  // 失活的组件钩子
      // global before hooks
      this.router.beforeHooks, // 全局 beforeEach 钩子
      // in-component update hooks
      extractUpdateHooks(updated), // 在当前路由改变，但是该组件被复用时调用
      // in-config enter guards
      activated.map(m => m.beforeEnter), // 需要渲染组件 enter 守卫钩子
      // async components
      resolveAsyncComponents(activated) // 解析异步路由组件
    )

    const iterator = (hook: NavigationGuard, next) => {
      if (this.pending !== route) { // 路由不相等就不跳转路由
        return abort(createNavigationCancelledError(current, route))
      }
      try {
        hook(route, current, (to: any) => { // 只有执行了钩子函数中的next，才会继续执行下一个钩子函数，否则会暂停跳转，以下逻辑是在判断 next() 中的传参
          if (to === false) {
            // next(false) -> abort navigation, ensure current URL
            this.ensureURL(true)
            abort(createNavigationAbortedError(current, route))
          } else if (isError(to)) {
            this.ensureURL(true)
            abort(to)
          } else if (
            typeof to === 'string' ||
            (typeof to === 'object' &&
              (typeof to.path === 'string' || typeof to.name === 'string'))
          ) {
            // next('/') or next({ path: '/' }) -> redirect
            abort(createNavigationRedirectedError(current, route))
            if (typeof to === 'object' && to.replace) {
              this.replace(to)
            } else {
              this.push(to)
            }
          } else {
            // confirm transition and pass on the value
            next(to)
          }
        })
      } catch (e) {
        abort(e)
      }
    }
    // ...
  }
  // ...
}

// dev/src/history/html5.js line 10
export class HTML5History extends History {
  _startLocation: string

  constructor (router: Router, base: ?string) {
    super(router, base)

    this._startLocation = getLocation(this.base)
  }

  setupListeners () { // 初始化
    if (this.listeners.length > 0) {
      return
    }

    const router = this.router
    const expectScroll = router.options.scrollBehavior
    const supportsScroll = supportsPushState && expectScroll

    if (supportsScroll) {
      this.listeners.push(setupScroll())
    }

    const handleRoutingEvent = () => {
      const current = this.current

      // Avoiding first `popstate` event dispatched in some browsers but first
      // history route not updated since async guard at the same time.
      const location = getLocation(this.base)
      if (this.current === START && location === this._startLocation) {
        return
      }

      this.transitionTo(location, route => {
        if (supportsScroll) {
          handleScroll(router, route, current, true)
        }
      })
    }
    window.addEventListener('popstate', handleRoutingEvent) // 事件监听
    this.listeners.push(() => {
      window.removeEventListener('popstate', handleRoutingEvent)
    })
  }

  go (n: number) {
    window.history.go(n)
  }

  push (location: RawLocation, onComplete?: Function, onAbort?: Function) {
    const { current: fromRoute } = this
    this.transitionTo(location, route => {
      pushState(cleanPath(this.base + route.fullPath))
      handleScroll(this.router, route, fromRoute, false)
      onComplete && onComplete(route)
    }, onAbort)
  }

  replace (location: RawLocation, onComplete?: Function, onAbort?: Function) {
    const { current: fromRoute } = this
    this.transitionTo(location, route => {
      replaceState(cleanPath(this.base + route.fullPath))
      handleScroll(this.router, route, fromRoute, false)
      onComplete && onComplete(route)
    }, onAbort)
  }

  ensureURL (push?: boolean) {
    if (getLocation(this.base) !== this.current.fullPath) {
      const current = cleanPath(this.base + this.current.fullPath)
      push ? pushState(current) : replaceState(current)
    }
  }

  getCurrentLocation (): string {
    return getLocation(this.base)
  }
}

参考

https://www.jianshu.com/p/557f2ba86892
https://juejin.im/post/6844904159678824456
https://juejin.im/post/6844904012630720526
https://juejin.im/post/6844904062698127367
https://developer.mozilla.org/zh-CN/docs/Web/API/History/pushState
https://liyucang-git.github.io/2019/08/15/vue-router%E6%BA%90%E7%A0%81%E5%88%86%E6%9E%90/
https://router.vuejs.org/zh/guide/essentials/history-mode.html#%E5%90%8E%E7%AB%AF%E9%85%8D%E7%BD%AE%E4%BE%8B%E5%AD%90