beforeRouteLeave (to, from, next) {
        console.log('離開(kāi)路路由')
       if(to.fullPath==='/home'){
         next();
       }else{
         next('/home')
       }

// 下面的寫法會(huì)死循環(huán)
     beforeRouteLeave (to, from, next) {
        console.log('離開(kāi)路路由')
       next('/home')
}

router.beforeEach((to, from, next) => {
  console.log('beforeEach');
  if(true){
    next('/');
  }else{
    next();
 }
});

router.beforeEach((to, from, next) => {
var userInfo= JSON. parse(sess ionStorage. getItem('userInfoStorage'));//獲取瀏覽器緩存的用戶信息
if(userInfo){//如果有就直接到首頁(yè)咯
next() ;
}else{
if(to. path==' /login' ){//如果是登錄頁(yè)面路徑，就直接next()
next() ;
}else{//不然就跳轉(zhuǎn)到登錄;
next(' /login');
}
}
});

// ('/')為登陸界面  
// next() 默認(rèn)跳轉(zhuǎn)to的path
if(isRequireAuthTrue){
    if(isLogin){
      console.log('導(dǎo)航守衛(wèi)保護(hù)');
      next(); //成功則跳轉(zhuǎn)
    }else {
      console.log('你還沒(méi)有登陸!');
      next({path:'/'}) //失敗則跳轉(zhuǎn)到登陸頁(yè)面
    }
  }else {
    next();//不需要導(dǎo)航守衛(wèi)的則直接next跳轉(zhuǎn)
  }

router.beforeEach((to, from, next) => {
    let {path} = to;
    if(path=== "/somewhere") {
        next(); // 導(dǎo)航目的地符合預(yù)期，繼續(xù)后續(xù)事情
     }else {
        next("/somewhere");  
        // 導(dǎo)航目的地不符合預(yù)期，重新路由新路徑地址，然后會(huì)再次觸發(fā)beforeEach鉤子并進(jìn)行二次判斷
    }
});

import Router from 'vue-router'
const router = new Router({
    {path: '/', component: index },
    {path: '/login', component: login},
    {path: '/error', component: error},
    {path: '*', component: error}
})

router.beforeEach((to, from, next) => {
    const isLogin = sessionStorage.getItem('loginData')
    if (isLogin) {
        next()
    } else {
        next('/error')
    } 
})

router.beforeEach((to, from, next) => {
    const isLogin = sessionStorage.getItem('loginData')
    if (isLogin) {
        next()
    } else {
        //next('/error')
        if (to.path === '/error') { //這就是跳出循環(huán)的關(guān)鍵
           next()
        } else {
            next('/error')
        }
    } 
})