VueRouter 对象

VueRouter 的实现是一个类，我们先对它做一个简单地分析，它的定义在 src/index.js 中：

export default class VueRouter {
  static install: () => void;
  static version: string;

  app: any;
  apps: Array<any>;
  ready: boolean;
  readyCbs: Array<Function>;
  options: RouterOptions;
  mode: string;
  history: HashHistory | HTML5History | AbstractHistory;
  matcher: Matcher;
  fallback: boolean;
  beforeHooks: Array<?NavigationGuard>;
  resolveHooks: Array<?NavigationGuard>;
  afterHooks: Array<?AfterNavigationHook>;

  constructor (options: RouterOptions = {}) {
    this.app = null
    this.apps = []
    this.options = options
    this.beforeHooks = []
    this.resolveHooks = []
    this.afterHooks = []
    this.matcher = createMatcher(options.routes || [], this)

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

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

  match (
    raw: RawLocation,
    current?: Route,
    redirectedFrom?: Location
  ): Route {
    return this.matcher.match(raw, current, redirectedFrom)
  }

  get currentRoute (): ?Route {
    return this.history && this.history.current
  }

  init (app: any) {
    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)

    if (this.app) {
      return
    }

    this.app = app

    const history = this.history

    if (history instanceof HTML5History) {
      history.transitionTo(history.getCurrentLocation())
    } else if (history instanceof HashHistory) {
      const setupHashListener = () => {
        history.setupListeners()
      }
      history.transitionTo(
        history.getCurrentLocation(),
        setupHashListener,
        setupHashListener
      )
    }

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

  beforeEach (fn: Function): Function {
    return registerHook(this.beforeHooks, fn)
  }

  beforeResolve (fn: Function): Function {
    return registerHook(this.resolveHooks, fn)
  }

  afterEach (fn: Function): Function {
    return registerHook(this.afterHooks, fn)
  }

  onReady (cb: Function, errorCb?: Function) {
    this.history.onReady(cb, errorCb)
  }

  onError (errorCb: Function) {
    this.history.onError(errorCb)
  }

  push (location: RawLocation, onComplete?: Function, onAbort?: Function) {
    this.history.push(location, onComplete, onAbort)
  }

  replace (location: RawLocation, onComplete?: Function, onAbort?: Function) {
    this.history.replace(location, onComplete, onAbort)
  }

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

  back () {
    this.go(-1)
  }

  forward () {
    this.go(1)
  }

  getMatchedComponents (to?: RawLocation | Route): Array<any> {
    const route: any = to
      ? to.matched
        ? to
        : this.resolve(to).route
      : this.currentRoute
    if (!route) {
      return []
    }
    return [].concat.apply([], route.matched.map(m => {
      return Object.keys(m.components).map(key => {
        return m.components[key]
      })
    }))
  }

  resolve (
    to: RawLocation,
    current?: Route,
    append?: boolean
  ): {
    location: Location,
    route: Route,
    href: string,
    normalizedTo: Location,
    resolved: Route
  } {
    const location = normalizeLocation(
      to,
      current || this.history.current,
      append,
      this
    )
    const route = this.match(location, current)
    const fullPath = route.redirectedFrom || route.fullPath
    const base = this.history.base
    const href = createHref(base, fullPath, this.mode)
    return {
      location,
      route,
      href,
      normalizedTo: location,
      resolved: route
    }
  }

  addRoutes (routes: Array<RouteConfig>) {
    this.matcher.addRoutes(routes)
    if (this.history.current !== START) {
      this.history.transitionTo(this.history.getCurrentLocation())
    }
  }
}

VueRouter 定义了一些属性和方法，我们先从它的构造函数看，当我们执行 new VueRouter 的时候做了哪些事情。

constructor (options: RouterOptions = {}) {
  this.app = null
  this.apps = []
  this.options = options
  this.beforeHooks = []
  this.resolveHooks = []
  this.afterHooks = []
  this.matcher = createMatcher(options.routes || [], this)

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

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

构造函数定义了一些属性，其中 this.app 表示根 Vue 实例，this.apps 保存持有 $options.router 属性的 Vue 实例，this.options 保存传入的路由配置，this.beforeHooks、 this.resolveHooks、this.afterHooks 表示一些钩子函数，我们之后会介绍，this.matcher 表示路由匹配器，我们之后会介绍，this.fallback 表示在浏览器不支持 history.pushState 的情况下，根据传入的 fallback 配置参数，决定是否回退到hash模式，this.mode 表示路由创建的模式，this.history 表示路由历史的具体的实现实例，它是根据 this.mode 的不同实现不同，它有 History 基类，然后不同的 history 实现都是继承 History。

实例化 VueRouter 后会返回它的实例 router，我们在 new Vue 的时候会把 router 作为配置的属性传入，回顾一下上一节我们讲 beforeCreate 混入的时候有这么一段代码：

beforeCreate() {
  if (isDef(this.$options.router)) {
    // ...
    this._router = this.$options.router
    this._router.init(this)
    // ...
  }
}  

所以组件在执行 beforeCreate 钩子函数的时候，如果传入了 router 实例，都会执行 router.init 方法：

init (app: any) {
  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)

  if (this.app) {
    return
  }

  this.app = app

  const history = this.history

  if (history instanceof HTML5History) {
    history.transitionTo(history.getCurrentLocation())
  } else if (history instanceof HashHistory) {
    const setupHashListener = () => {
      history.setupListeners()
    }
    history.transitionTo(
      history.getCurrentLocation(),
      setupHashListener,
      setupHashListener
    )
  }

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

init 的逻辑很简单，它传入的参数是 Vue 实例，然后存储到 this.apps 中；只有根 Vue 实例会保存到 this.app 中，并且会拿到当前的 this.history，根据它的不同类型来执行不同逻辑，由于我们平时使用 hash 路由多一些，所以我们先看这部分逻辑，先定义了 setupHashListener 函数，接着执行了 history.transitionTo 方法，它是定义在 History 基类中，代码在 src/history/base.js：

transitionTo (location: RawLocation, onComplete?: Function, onAbort?: Function) {
  const route = this.router.match(location, this.current)
  // ...
}

我们先不着急去看 transitionTo 的具体实现，先看第一行代码，它调用了 this.router.match 函数：

match (
  raw: RawLocation,
  current?: Route,
  redirectedFrom?: Location
): Route {
  return this.matcher.match(raw, current, redirectedFrom)
}

实际上是调用了 this.matcher.match 方法去做匹配，所以接下来我们先来了解一下 matcher 的相关实现。

总结

通过这一节的分析，我们大致对 VueRouter 类有了大致了解，知道了它的一些属性和方法，同时了解到在组件的初始化阶段，执行到 beforeCreate 钩子函数的时候会执行 router.init 方法，然后又会执行 history.transitionTo 方法做路由过渡，进而引出了 matcher 的概念，接下来我们先研究一下 matcher 的相关实现。