let vm = new Vue({
 el: "#app",
 data: {},
 router,
 watch: {
 '$route.path': function (newVal, oldVal) {
 if (newVal === '/login') {
 console.log('歡迎進(jìn)入登錄頁面');
 }
 if (newVal === '/register') {
 console.log('歡迎進(jìn)入注冊頁面');
 }
 }
 }
})

watch:{ //監(jiān)聽路由變化
 $route( to , from ){ 
 console.log( to , from )
 // to , from 分別表示從哪跳轉(zhuǎn)到哪，都是一個對象
 // to.path ( 表示的是要跳轉(zhuǎn)到的路由的地址 eg: /home );
 }
}