javascript async call example

gistfile1.txt

var cheerio = require('cheerio');
var request = require('request');
var async = require('async');
var q = require('q');
var _ = require('underscore');

var testCase = [
  'http://www.baidu.com',
  'http://www.amazon.com',
  'http://www.youku.com',
  'http://www.github.com'
];

function getTitles(urls, callback) {
  async.parallel(urls.map(function (url) {
    return function (callback) {
      request(url, function (err, res, body) {
        var $ = cheerio.load(body);
        callback(err, $('title').text());
      });
    };
  }), callback);
}

function getTitles2(urls) {
  return q.all(urls.map(function (url) {
    return q.nfcall(request, url);
  })).spread(function () {
    return _.map(arguments, function (result) {
      var $ = cheerio.load(result[1]);
      return $('title').text();
    });
  });
}

function getTitles3(urls) {
  var tasks = urls.map(function (url) {
    var deferred = q.defer();
    request(url, function (err, res, body) {
      if (err) {
        deferred.reject(err);
        return;
      }
      deferred.resolve([res, body]);
    });
    return deferred.promise;
  });

  var promise = q.all(tasks);
  promise.spread(function () {
    var result = _.map(arguments, function (reply) {
      var body = reply[1];
      var $ = cheerio.load(body);
      var title = $('title').text();
      return title;
    });
    return result;
  });

}

getTitles(testCase, function (err, result) {
  console.log(result);
});


getTitles2(testCase).then(function (result) {
  console.log(result);
});