Vue路由Hash模式分析
阿新 • • 發佈：2020-10-04
# Vue路由Hash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，即使用`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。
## 描述
`Hash`符號即`#`原本的目的是用來指示`URL`中指示網頁中的位置，例如`https://www.example.com/index.html#print`即代表`example`的`index.html`的`print`位置，瀏覽器讀取這個`URL`後，會自動將`print`位置滾動至可視區域，通常使用``標籤的`name`屬性或者``標籤的`id`屬性指定錨點。
通過`window.location.hash`屬效能夠讀取錨點位置，可以為`Hash`的改變新增`hashchange`監聽事件，每一次改變`Hash`，都會在瀏覽器的訪問歷史中增加一個記錄，此外`Hash`雖然出現在`URL`中，但不會被包括在`HTTP`請求中，即`#`及之後的字元不會被髮送到服務端進行資源或資料的請求，其是用來指導瀏覽器動作的，對伺服器端沒有效果，因此改變`Hash`不會重新載入頁面。
`Vue-router`的作用就是通過改變`URL`，在不重新請求頁面的情況下，更新頁面檢視，從而動態載入與銷燬元件，簡單的說就是，雖然位址列的地址改變了，但是並不是一個全新的頁面，而是之前的頁面某些部分進行了修改，這也是`SPA`單頁應用的特點，其所有的活動侷限於一個`Web`頁面中，非懶載入的頁面僅在該`Web`頁面初始化時載入相應的`HTML`、`JavaScript`、`CSS`檔案，一旦頁面載入完成，`SPA`不會進行頁面的重新載入或跳轉，而是利用`JavaScript`動態的變換`HTML`，預設`Hash`模式是通過錨點實現路由以及控制組件的顯示與隱藏來實現類似於頁面跳轉的互動。
## 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)`，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
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)
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: "${record.path}" }`
)
}
}
}
```
在上文的建構函式中例項化的`HashHistory`物件就是對於`Hash`模式下的路由的處理，主要是通過繼承`History`物件以及自身實現的方法完成路由，以及針對於不支援`history api`的相容處理，以及保證預設進入的時候對應的`Hash`值是以`/`開頭的，如果不是則替換。在初始化`VueRouter`時呼叫的`init`方法呼叫了路由切換以及呼叫了`setupListeners`方法實現了路由的切換的監聽回撥，注意此時並沒有在`HashHistory`物件的建構函式中直接新增事件監聽，這是為了修復`vuejs/vue-router#725`的問題，簡要來說就是說如果在`beforeEnter`這樣的鉤子函式中是非同步的話，`beforeEnter`鉤子就會被觸發兩次，原因是因為在初始化的時候如果此時的`hash`值不是以`/`開頭的話就會補上`#/`，這個過程會觸發`hashchange`事件，所以會再走一次生命週期鉤子，也就意味著會再次呼叫`beforeEnter`鉤子函式。
```javascript
// dev/src/index.js line 21
export default class VueRouter {
//...
init (app: any /* Vue component instance */) {
process.env.NODE_ENV !== 'production' &&
assert(
install.installed,
`not installed. Make sure to call \`Vue.use(VueRouter)\` ` +
`before creating root instance.`
)
this.apps.push(app)
// set up app destroyed handler
// https://github.com/vuejs/vue-router/issues/2639
app.$once('hook:destroyed', () =>