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。