javascript - 返回值之前等待异步回调

Question

与

文件A

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

文件B

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

如何让 console.log userID('someUsername') 也输出 ID，而不是 0？ IE。在返回 id 之前让它等待。

我尝试过使用 Meteor.wrapAsync 和 Meteor.bindEnvironment 随机包装内容，但似乎无济于事。

Answer 1

您可以在回调中完成工作，也可以使用 Promise 或事件发射器控制流程:

"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);
}