如何将一个承诺延迟到async.每一个完成

How to delay a promise until async.each completes?

本文关键字：async 每一个迟到延迟一个承诺更新时间：2023-09-26

如何将承诺延迟到异步操作完成?我正在使用异步和蓝鸟库。一旦我启动我的程序，done()函数返回一个错误，它是一个空的或几乎空的'masterlist'对象。为什么async不等待迭代器完成它的操作?

// bundler.js
var masterlist = {
   "children": []
 , "keywords": []
 , "mentions": 0
 , "name" : "newsfeed"
 , "size" : 0
}
// initialize() returns a promise with the populated masterlist
exports.initialize = function() {
  return new Promise(function(resolve, reject) {
    // pullBreakingNews() returns a promise with the breaking news articles
    nytimes.pullBreakingNews().then(function(abstracts) {
      async.map(abstracts, iterator, done);
      function iterator(item, callback) {
        alchemyapi.entities('text', item, {}, function(response) {
          // initialize each entity with masterlist
          response.entities.forEach(function(entity) {
            masterlist.children[masterlist.children.length] =
             {
                 "abstract": item
               , "children": []
               , "name": entity.text
               , "size": 0
             };
            masterlist.size += 1;
            masterlist.keywords.push(entity.text);
          });
          callback(masterlist);
        });
      };
      function done(err, results) {
        if (err) {
          console.log("ERROR: ", err);
        } else {
          resolve(results);
        }
      };
    });
  });
};

Firehose.js是调用initializer()的模块。我相信firehose会先运行，promise会在这个过程中被调用。Server.js => firehose.js => bundler.js => nytimes api

// firehose.js
// Compares entities to Twitter stream, counts every match
exports.aggregator = function(callback) {
  bundler.initialize().then(function(masterlist) {
    t.stream('statuses/filter', { track: masterlist.keywords }, function(stream) {
      // read twitter firehose for incoming tweets.
      stream.on('data', function(tweet) {
        var tweetText = tweet.text.toLowerCase();
        // sift through each tweet for presence of entities
        masterlist.children.forEach(function(parentObject) {
          // if the entity exists in the tweet, update counters
          if (tweetText.indexOf(parentObject.name.toLowerCase()) !== -1) {
            parentObject.size += 1;
            masterlist.mentions += 1;
            callback(masterlist);
          }
        });
      });
    });
  });
};

非常感谢您的帮助

请不要把回调和承诺混在一起，只使用其中之一

// Do this somewhere else, it is only needed once
// it adds promise returning versions of all alchemy methods for you
Promise.promisifyAll(require('alchemy-api').prototype);
exports.initialize = function() {
  return nytimes.pullBreakingNews().map(function(abstract) {
    // Note that it is entitiesAsync that is a promise returning function 
    return alchemyapi.entitiesAsync('text', abstract, {}).then(function(response){
      response.entities.forEach(function(entity) {
            masterlist.children[masterlist.children.length] =
             {
                 "abstract": abstract
               , "children": []
               , "name": entity.text
               , "size": 0
             };
            masterlist.size += 1;
            masterlist.keywords.push(entity.text);
      });
    });
  }).return(masterlist);
};

并且你的initialize函数没有检查它是否已经初始化

迭代器的回调函数接受错误作为第一个参数。如果没有错误，您应该在那里传递一个假值(如null)而不是masterlist。

function iterator(item, callback) {
    alchemyapi.entities('text', item, {}, function(response) {
      // initialize each entity with masterlist
      response.entities.forEach(function(entity) {
        masterlist.children[masterlist.children.length] =
         {
             "abstract": item
           , "children": []
       , "name": entity.text
       , "size": 0
         };
        masterlist.size += 1;
        masterlist.keywords.push(entity.text);
      });
      callback(null, masterlist);
    });
  };