同步请求

let myFirstPromise = new Promise((resolve, reject) => {
  // We call resolve(...) when what we were doing asynchronously was successful, and reject(...) when it failed.
  // In this example, we use setTimeout(...) to simulate async code. 
  // In reality, you will probably be using something like XHR or an HTML5 API.
  setTimeout( function() {
    resolve("Success!")  // Yay! Everything went well!
  }, 250) 
}) 

myFirstPromise.then((successMessage) => {
  // successMessage is whatever we passed in the resolve(...) function above.
  // It doesn't have to be a string, but if it is only a succeed message, it probably will be.
  console.log("Yay! " + successMessage) 
});

export function getRoutes() {
  return request({
    url: '/vue-element-admin/routes',
    method: 'get'
  })
}

import { getRoutes, getRoles, addRole, deleteRole, updateRole } from '@/api/role'

methods: {
    async getRoutes() {
      const res = await getRoutes() //会执行完这句再执行下面.
      this.serviceRoutes = res.data
      this.routes = this.generateRoutes(res.data)
    },
    async getRoles() {
      const res = await getRoles()
      this.rolesList = res.data
    },
}