如何在angularjs服务中返回异步调用的响应？

Question

我已经阅读了How do I return the response from an asynchronous call?这个问题的答案但是我不确定我是否理解，我认为我的问题有点不同。我改变我的服务是这样的：

.service('CommonService',['$firebase', function($firebase){ 

var username; 

function onComplete(result){ 
    username = result; 
}; 

var getData = function(){ 

    var ref = new Firebase("https://instafame.firebaseio.com"); 

    ref.onAuth(function(authData){ 
     var userid = authData.uid; 
     console.log(userid); 

     var newref = new Firebase("https://instafame.firebaseio.com/users/" + userid) 

     newref.once("value", function(snapshot) { 
      var data = snapshot.val() 
      newUsername = data.username; 
      callback(newUsername); 

     }) 
    }); 
    }; 

    return{ 
     getUsername: function(){ 
      getData(onComplete); 
      return username;} 
    }; 
}]) 

在我的控制器I存储变量user内CommonService的回报：

var user = CommonService.getUsername(); 
console.log(user); 

的问题是，控制台仍返回“未定义” 。我试图根据这些建议更改代码，但它没有运行。我该怎么办？

在此先感谢

Answer 1

异步/等待

我们需要提供一种方式来等待您的请求作出回应。我们可以使用async/await来做到这一点，并让我们做出承诺，以解决我们正在检索的价值;

.service('CommonService',['$firebase', function($firebase){ 

var username; 
var getData = function(){  //declare this function as an async 

    return new Promise((resolve, reject) => { 

     var ref = new Firebase("https://instafame.firebaseio.com"); 

     ref.onAuth(function(authData){ 
      var userid = authData.uid; 
      console.log(userid); 

      var newref = new Firebase("https://instafame.firebaseio.com/users/" + userid) 

      newref.once("value", function(snapshot) { 
       var data = snapshot.val() 
       newUsername = data.username; 
       !!newUsername 
        ? 
       resolve(newUsername) 
        : 
       reject('Error: No username found'); 
      }) 

     }); 
    }; 
}; 

    return{ 
     getUsername: async function(){ 
      username = await getData(); //await will pause execution of the code here until getData() returns a value. 
      return username; 
     } 
    }; 
}])