beforeRouteEnter(to, from, next) {
   //判斷從index頁(yè)面進(jìn)入，將list的isBack設(shè)置為true
   //這樣就可以請(qǐng)求數(shù)據(jù)了
     if (from.name == 'index') {
      to.meta.isBack = true;
     }
     next();
   },
   activated: function () {
     if (this.$route.meta.isBack || this.isFirstEnter) {
      //清理已有商品列表的數(shù)據(jù)，重新請(qǐng)求數(shù)據(jù)，如果不清除的話(huà)就會(huì)有之前的商品緩存，延遲顯示最新的商品
      this.proData = [];
      //請(qǐng)求數(shù)據(jù)
      this.fetchData();
     }
     //重新設(shè)置當(dāng)前路由的isBack
     this.$route.meta.isBack = false;
     //重新設(shè)置是否第一次進(jìn)入
     this.isFirstEnter = false;
   },
   mounted: function () {
    //如果是第一次進(jìn)入，或者刷新操作的話(huà)，也請(qǐng)求數(shù)據(jù)
     this.isFirstEnter = true;
   },

const appRouter = {
 mode: "history",
 base: "/m/",
 routes: [
  {
   path: "",
   redirect: "/index"
  },
  {
   path: "/index",
   name: "index",
   component: Index,
   meta: {
    keepAlive: true
   }
  },
    {
   path: "/list",
   name: "list",
   component: List,
   meta: {
    keepAlive: true,
    isBack: false //isback是true的時(shí)候請(qǐng)求數(shù)據(jù)，或者第一次進(jìn)入的時(shí)候請(qǐng)求數(shù)據(jù)
   }
  },
  {
   path: "/product/:id",
   name: "product",
   component: Product,
   meta: {
    keepAlive: false
   }
  }
  
 ]
};

Vue.use(Router);
export default new Router(appRouter);