如何使用promises等待异步API调用(How to use promises to wait for async API calls)

 我正在创建一个API，当GET对新闻API进行一系列调用时，新闻文章标题被提取到一个巨大的字符串中，并且该字符串被处理成一个对象，以便传递给前端的wordcloud。 到目前为止，我已经能够使用下划线的_.after和request-promise使我的应用程序等到所有API调用完成后再调用processWordBank() ，它接受巨型字符串并将其清理成对象。 但是，一旦processWordBank() ，我就不明白程序的流程在哪里。 理想情况下， processWordBank()将obj返回到路由器中的cloudObj，以便obj可以传递给res.json()并作为响应吐出。 我相信我对_.after使用让我陷入了一种奇怪的境地，但这是我能够在进行下一个所需动作之前完成异步调用的唯一方法。 有什么建议么？ 
 
 （我试图省略所有不必要的代码，但如果这还不够，请告诉我） 
 
// includes...
var sourceString = ""
// router
export default ({ config }) => {
  let news = Router()
  news.get('/', function(req, res){
    var cloudObj = getSources()
        res.json({ cloudObj })
  })
  return news
}

// create list of words (sourceString) by pulling news data from various sources
function getSources() {
    return getNewsApi()

}
// NEWS API
// GET top 10 news article titles from News API (news sources are determined by the values of newsApiSource array)
function getNewsApi() {
  var finished = _.after(newsApiSource.length, processWordBank)
  for(var i = 0; i < newsApiSource.length; i++) {
    let options = {
      uri: 'https://newsapi.org/v1/articles?source=' + newsApiSource[i] + '&sortBy=' + rank + '&apiKey=' + apiKey,
      json: true
    }
    rp(options)
    .then(function (res) {
      let articles = res.articles // grab article objects from the response
      let articleTitles = " " + _.pluck(articles, 'title') // extract title of each news article
      sourceString += " " + articleTitles // add all titles to the word bank
      finished() // this async task has finished
    })
    .catch(function (err) {
      console.log(err)
    })
    }
}

// analyse word bank for patterns/trends
function processWordBank(){
  var sourceArray = refineSource(sourceString)
  sourceArray = combineCommon(sourceArray)
  sourceArray = getWordFreq(sourceArray)
  var obj = sortToObject(sourceArray[0], sourceArray[1])
  console.log(obj)
  return obj
}

I am creating an API that when GET, a series of calls to the News API are made, news article titles are extracted into a giant string, and that string is processed into an object to be delivered to a wordcloud on the front-end. So far, I've been able to use underscore's _.after and request-promise to make my app wait till all API calls have completed before calling processWordBank() which takes the giant string and cleans it up into an object. However, once processWordBank() is called, I don't understand where the flow of the program is. Ideally, processWordBank() returns obj to cloudObj in the router, so that the obj can be passed to res.json() and spit out as the response. I believe my use of _.after has put me in a weird situation, but it's the only way I've been able to get async calls to finish before proceeding to next desired action. Any suggestions?
 
(I've tried to leave out all unnecessary code but let me know if this is insufficient) 
 
// includes...
var sourceString = ""
// router
export default ({ config }) => {
  let news = Router()
  news.get('/', function(req, res){
    var cloudObj = getSources()
        res.json({ cloudObj })
  })
  return news
}

// create list of words (sourceString) by pulling news data from various sources
function getSources() {
    return getNewsApi()

}
// NEWS API
// GET top 10 news article titles from News API (news sources are determined by the values of newsApiSource array)
function getNewsApi() {
  var finished = _.after(newsApiSource.length, processWordBank)
  for(var i = 0; i < newsApiSource.length; i++) {
    let options = {
      uri: 'https://newsapi.org/v1/articles?source=' + newsApiSource[i] + '&sortBy=' + rank + '&apiKey=' + apiKey,
      json: true
    }
    rp(options)
    .then(function (res) {
      let articles = res.articles // grab article objects from the response
      let articleTitles = " " + _.pluck(articles, 'title') // extract title of each news article
      sourceString += " " + articleTitles // add all titles to the word bank
      finished() // this async task has finished
    })
    .catch(function (err) {
      console.log(err)
    })
    }
}

// analyse word bank for patterns/trends
function processWordBank(){
  var sourceArray = refineSource(sourceString)
  sourceArray = combineCommon(sourceArray)
  sourceArray = getWordFreq(sourceArray)
  var obj = sortToObject(sourceArray[0], sourceArray[1])
  console.log(obj)
  return obj
}

原文：https://stackoverflow.com/questions/42340237