等待异步回调返回值

问题描述：

的fileA之前

userID = (userName) -> 
    id = 0 
    someAPI.getUser userName, (err, data, res) -> 
    id = data.id if data 
    console.log id # Outputs ID 
    return 
    id 

console.log userID('someUsername') # Outputs 0

FILEB

getUser: (username, callback) -> 
    return api.get 'users/show', { 'username': username }, callback

我怎样才能console.log userID('someUsername')输出ID为好，而不是0？即请在返回ID之前等待。

我曾尝试随机包装与Meteor.wrapAsync和Meteor.bindEnvironment的东西，但似乎无法得到任何地方。

把它放在'someAPI.getUser'的回调中。 – Pointy 2014-10-01 15:22:11

欢迎来到异步的奇妙世界，你不能那样做。请参阅相关http://stackoverflow.com/q/23667086/1331430 – 2014-10-01 15:29:25

与流星相关的答案是使用期货。阅读[this]（https://www.discovermeteor.com/patterns/5828399）和[this]（https://gist.github.com/possibilities/3443021）。 – richsilv 2014-10-01 15:41:49

答

谢谢大家。我发现一个解决方案使用https://github.com/meteorhacks/meteor-async

getUserID = Async.wrap((username, callback) -> 
    someAPI.getUser username, (err, data, res) -> 
    callback err, data.id 
) 

console.log getUserID('someUsername')

答

您可以做到在回调的工作或控制与承诺或事件发射流程：

"use strict"; 

var Q = require('q'); 
var EventEmitter = require('events').EventEmitter; 

// using a promise 
var defer = Q.defer(); 

// using an emitter 
var getUserID = new EventEmitter(); 

var id = 0; 
getUser("somename", function (err, data, res) { 
    if (data) 
     id = data.id; 
    // simply do the work in the callback 
    console.log("In callback: "+data.id); 
    // this signals the 'then' success callback to execute 
    defer.resolve(id); 
    // this signals the .on('gotid' callback to execute 
    getUserID.emit('gotid', id); 
}); 

console.log("oops, this is async...: "+id); 

defer.promise.then(
    function (id) { 
     console.log("Through Promise: "+id); 
    } 
); 

getUserID.on('gotid', 
      function (id) { 
       console.log("Through emitter: "+id); 
      } 
      ); 

function getUser (username, callback) { 
    setTimeout(function() { 
     callback(null, { id : 1234 }, null); 
    }, 100); 
}

等待异步回调返回值

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