Vue路由History模式分析
阿新 • • 發佈：2020-10-10
# Vue路由History模式分析
`Vue-router`是`Vue`的核心元件，主要是作為`Vue`的路由管理器，`Vue-router`預設`hash`模式，通過引入`Vue-router`物件模組時配置`mode`屬性可以啟用`history`模式。
## 描述
`Vue-router`的`hash`模式使用`URL`的`Hash`來模擬一個完整的`URL`，當`URL`改變時頁面不會重新載入，而`Vue-router`的`history`模式是充分利用`history.pushState`的`API`來完成`URL`跳轉，同樣在頁面跳轉時無須重新載入頁面，當然也不會對於服務端進行請求，當然對於`history`模式仍然是需要後端的配置支援，由於應用是個單頁客戶端應用，如果後臺沒有正確的配置，當用戶在瀏覽器直接訪問`URL`時就會返回`404`，所以需要在服務端增加一個覆蓋所有情況的候選資源，如果`URL`匹配不到任何靜態資源時，則應該返回同一個`index.html`應用依賴頁面，例如在`Nginx`下的配置。
```
location / {
try_files $uri $uri/ /index.html;
}
```
## 分析
`Vue-router`原始碼的實現比較複雜，會處理各種相容問題與異常以及各種條件分支，文章分析比較核心的程式碼部分，精簡過後的版本，重要部分做出註釋，`commit id`為`560d11d`。
首先是在定義`Router`時呼叫`Vue.use(VueRouter)`，這是`Vue.js`外掛的經典寫法，給外掛物件增加`install`方法用來安裝外掛具體邏輯，此時會呼叫`VueRouter`類上的靜態方法，即`VueRouter.install = install`，`install`模組主要是保證`Vue-router`只被`use`一次，以及通過`mixin`在`Vue`的生命週期`beforeCreate`內註冊例項，在`destroyed`內銷燬例項，還有定義`$router`與`$route`屬性為只讀屬性以及``與``全域性元件的註冊。
```javascript
// dev/src/install.js line 6
export function install (Vue) {
if (install.installed && _Vue === Vue) return
install.installed = true // 保證 Vue-router 只被 use 一次
_Vue = Vue
const isDef = v => v !== undefined
const registerInstance = (vm, callVal) => {
let i = vm.$options._parentVnode
if (isDef(i) && isDef(i = i.data) && isDef(i = i.registerRouteInstance)) {
i(vm, callVal)
}
}
Vue.mixin({
beforeCreate () { // 註冊例項
if (isDef(this.$options.router)) { // this.$options.router 來自於 VueRouter 的例項化 // 判斷例項是否已經掛載
this._routerRoot = this
this._router = this.$options.router
this._router.init(this) // // 呼叫 VueRouter 的 init 方法 // 後文會說明 init 方法的作用
Vue.util.defineReactive(this, '_route', this._router.history.current)
} else {
this._routerRoot = (this.$parent && this.$parent._routerRoot) || this // 將元件的 _routerRoot 都指向根 Vue 例項
}
registerInstance(this, this)
},
destroyed () { // 銷燬例項 即掛載undefined
registerInstance(this)
}
})
Object.defineProperty(Vue.prototype, '$router', {
get () { return this._routerRoot._router }
})
Object.defineProperty(Vue.prototype, '$route', {
get () { return this._routerRoot._route }
})
Vue.component('RouterView', View) // 註冊全域性元件
Vue.component('RouterLink', Link) // 註冊全域性元件
const strats = Vue.config.optionMergeStrategies
// use the same hook merging strategy for route hooks
strats.beforeRouteEnter = strats.beforeRouteLeave = strats.beforeRouteUpdate = strats.created
}
```
之後是`VueRouter`物件的建構函式，主要是先獲取`mode`的值，如果`mode`的值為`history`但是瀏覽器不支援`history`模式,那麼就強制設定`mode`值為`hash`，接下來根據`mode`的值，來選擇`vue-router`使用哪種模式。
```javascript
// 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) // 建立路由匹配物件
let mode = options.mode || 'hash'
this.fallback =
mode === 'history' && !supportsPushState && options.fallback !== false // 檢車相容
if (this.fallback) {
mode = 'hash'
}
if (!inBrowser) {
mode = 'abstract'
}
this.mode = mode
switch (mode) {
case 'history':
this.history = new HTML5History(this, options.base) // 例項化history模式
break
case 'hash':
this.history = new HashHistory(this, options.base, this.fallback) // 例項化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: ${mode}`)
}
}
}
```
在建構函式中呼叫了建立路由匹配物件的方法`createMatcher`，而在`createMatcher`中又呼叫了實際用以建立路由對映表的方法`createRouteMap`，可以說`createMatcher`函式的作用就是建立路由對映表，然後通過閉包的方式讓`addRoutes`和`match`函式能夠使用路由對映表的幾個物件，最後返回一個`Matcher`物件。
```javascript
// dev/src/create-matcher.js line 16
export function createMatcher (
routes: Array,
router: VueRouter
): Matcher {
const { pathList, pathMap, nameMap } = createRouteMap(routes) // 建立路由對映表
function addRoutes (routes) {
createRouteMap(routes, pathList, pathMap, nameMap)
}
function match ( // 路由匹配
raw: RawLocation,
currentRoute?: Route,
redirectedFrom?: Location
): Route {
const location = normalizeLocation(raw, currentRoute, false, router) // location 是一個物件，類似於 {"_normalized":true,"path":"/","query":{},"hash":""}
const { name } = location
if (name) { // 如果有路由名稱 就進行nameMap對映
const record = nameMap[name] // nameMap[name] = 路由記錄
if (process.env.NODE_ENV !== 'production') {
warn(record, `Route with name '${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裡匹配到路由記錄
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 ( // 處理重定向
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: ${JSON.stringify(redirect)}`)
}
return _createRoute(null, location)
}
}
function alias ( // 處理別名
record: RouteRecord,
location: Location,
matchAs: string
): Route {
const aliasedPath = fillParams(matchAs, location.params, `aliased route with path "${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 ( // 建立路由
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) // 建立路由物件
}
return {
match,
addRoutes
}
}
// dev/src/create-route-map.js line 7
export function createRouteMap (
routes: Array,
oldPathList?: Array,
oldPathMap?: Dictionary,
oldNameMap?: Dictionary
): {
pathList: Array,
pathMap: Dictionary,
nameMap: Dictionary
} {
// the path list is used to control path matching priority
const pathList: Array = oldPathList || [] // 建立對映表
// $flow-disable-line
const pathMap: Dictionary = oldPathMap || Object.create(null)
// $flow-disable-line
const nameMap: Dictionary = oldNameMap || Object.create(null)
routes.forEach(route => { // 遍歷路由配置，為每個配置新增路由記錄
addRouteRecord(pathList, pathMap, nameMap, route)
})
// ensure wildcard routes are always at the end
for (let i = 0, l = pathList.length; i < l; i++) { // 確保萬用字元在最後
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 => ,
pathMap: Dictionary,
nameMap: Dictionary,
route: RouteConfig,
parent?: RouteRecord,
matchAs?: string
) {
const { path, name } = route // 獲得路由配置下的屬性
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: ${String(
path || name
)} cannot be a ` + `string id. Use an actual component instead.`
)
}
const pathToRegexpOptions: PathToRegexpOptions =
route.pathToRegexpOptions || {}
const normalizedPath = normalizePath(path, parent, pathToRegexpOptions.strict)
if (typeof route.caseSensitive === 'boolean') {
pathToRegexpOptions.sensitive = route.caseSensitive
}
const record: RouteRecord = { // 生成記錄物件
path: normalizedPath,
regex: compileRouteRegex(normalizedPath, pathToRegexpOptions),
components: route.components || { default: route.component },
instances: {},
name,
parent,
matchAs,
redirect: route.redirect,
beforeEnter: route.beforeEnter,
meta: route.meta || {},
props:
route.props == null
? {}
: route.components
? route.props
: { default: route.props }
}
if (route.children) {
// Warn if route is named, does not redirect and has a default child route.
// If users navigate to this route by name, the default child will
// not be rendered (GH Issue #629)
if (process.env.NODE_ENV !== 'production') {
if (
route.name &&
!route.redirect &&
route.children.some(child => /^\/?$/.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 => { // 遞迴路由配置的 children 屬性，新增路由記錄
const childMatchAs = matchAs
? cleanPath(`${matchAs}/${child.path}`)
: undefined
addRouteRecord(pathList, pathMap, nameMap, child, record, childMatchAs)
})
}
if (!pathMap[record.path]) { // 如果有多個相同的路徑，只有第一個起作用，後面的會被忽略
pathList.push(record.path)
pathMap[record.path] = record
}
if (route.alias !== undefined) { // 如果路由有別名的話，給別名也新增路由記錄
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: "${record.path}" }`
)
}
}
}
```
在上文的建構函式中例項化的`HTML5History`物件就是對於`history`模式下的路由的處理，主要是通過繼承`History`物件以及自身實現的方法完成路由。在初始化`VueRouter`時呼叫的`init`方法呼叫了路由切換以及呼叫了`setupListeners`方法實現了路由的切換的監聽回撥，注意此時並沒有在`HTML5History`物件的建構函式中直接新增事件監聽，這是因為需要避免在某些瀏覽器中排程第一個`popstate`事件，但是由於非同步保護，第一個歷史記錄路由未同時更新的問題。`history`模式的程式碼結構以及更新檢視的邏輯與`hash`模式基本類似，主要是監聽`popstate`事件以及對於`push()`和`replace()`方法的變動，使用`History`物件的`pushState()`與`replaceState()`等方法進行路由的變換。
```javascript
// dev/src/index.js line 21
export default class VueRouter {
//...
init (app: any /* Vue component instance */) {
process.env.NODE_ENV !== 'production' &&
assert(
install.installed,
`not installed. Make sure to call \`Vue.use(VueRouter)\` ` +
`before creating root instance.`
)
this.apps.push(app)
// set up app destroyed handler
// https://github.com/vuejs/vue-router/issues/2639
app.$once('hook:destroyed', () =>