new Vue({
  data: {
    userId: 1
  },
  computed: {
    username: {
      // Using vue-resource
      return Vue.http.get('/get-username-by-id/' + this.userId)
        // This assumes that this endpoint will send us a response
        // that contains something like this:
        // { 
        //   "username": "username-goes-here"
        // }
        .then(response => response.data.username)
    }
  }
}

new Vue({
  data: {
    userId: 1
  },
  asyncComputed: {
    username: {
      return Vue.http.get('/get-username-by-id/' + this.userId)
        .then(response => response.data.username)
    }
  }
}

new Vue({
  asyncComputed: {
    async someCalculation () {
      const x = await someAsycFunction()
      const y = await anotherAsyncFunction()
      return x + y
    }
  }
})

import AsyncComputed from 'vue-async-computed'

/* Initialize the plugin */
Vue.use(AsyncComputed)

/*
   Then, when you create a Vue instance (or component),
   you can pass an object named "asyncComputed" as well as
   or instead of the standard "computed" option. The functions
   you pass to "asyncComputed" should return promises, and the values
   those promises resolve to are then asynchronously bound to the
   Vue instance as they resolve. Just as with normal computed
   properties, if the data the property depends on changes
   then the property is re-run automatically.
   
   You can almost completely ignore the fact that behind the
   scenes they are asynchronous. The one thing to remember is
   that until a asynchronous property's promise resolves
   for the first time, the value of the computed property is null.
*/

const vm = new Vue({
  data: {
    x: 2,
    y: 3
  },
  asyncComputed: {
    sum () {
      const total = this.x + this.y
      return new Promise(resolve =>
        setTimeout(() => resolve(total), 1000)
      )
    }
  }
})

/*
   Until one second has passed, vm.sum will be null.  After that,
   vm.sum will be 5. If you change vm.x or vm.y, then one
   second later vm.sum will automatically update itself to be
   the sum of the values to which you set vm.x and vm.y the previous second.
*/

Vue.use(AsyncComputed, {
  errorHandler (msg) {
    console.log('Hey, an error!')
    console.log('---')
    console.log(msg)
  }
)