node.js：使http调用for循环

Question

I want to make an http call for each element in an array, and combine all the responses into a single array, like so:

result = [] ; i = 0
for item in array
  options = get_options(item)
  request options, (err, res, body)->
    result[i++] = body

// when all calls are done, console.log the 'result' array

I'm looking at the async module, but I'm not really sure how to use it.

Answer 1

Try this, should work. You may want to try mapLimit to limit the no of parallel requests or mapSeries to do it in order.

var async = require('async');
var request = require('request');
async.map(['url1', 'url2'], function(item, callback){
  request(item, function (error, response, body) {
    callback(error, body);
  });
}, function(err, results){
  console.log(results);
});

for your example I need to see your get_options function. is it synchronous? if yes you can do this

var async = require('async');
var request = require('request');
var options;
async.map([item1, item2], function(item, callback){
  options = get_options(item);
  request(options, function (error, response, body) {
    callback(error, body);
  });
}, function(err, results){
  console.log(results);
});

If your get_options is asynchronous and accepts callback do following:

var async = require('async');
var request = require('request');
async.map([item1, item2], function(item, callback){
  get_options(item, function(err, option){
    if(err) {
      callback(err);
    }
    else{
      request(options, function (error, response, body) {
       callback(error, body);
      });
    }
  });
}, function(err, results){
  console.log(results);
});

Answer 2

using async library's map function you can

var makeRequest = function(item, callback){
    var options = get_options(item);
    // handle http errors and getting access to body properly
    http.get(options,res){
        callback(null, res)
    }
}

async.map(['item1','item2','item3'], makeRequest(item, callback), function(err, results){
    //check errors do stuff with results
});

Answer 3

If you're interested in using promises here is an answer for that as well:

var Q = require('q');
var http = require('http');

var httpGet = function(url) {
  var data = "", defer = Q.defer();
  http.get(url, function (res) {
    var content_length = parseInt(res.headers['content-length'], 10);
    var total_downloaded = 0;
    if (res.statusCode !== 200) {
      defer.reject("HTTP Error " + res.statusCode + " for " + url);
      return;
    }
    res.on("error", defer.reject);
    res.on("data", function (chunk) {
      data += chunk;
      total_downloaded += chunk.length;
      var percentage = Math.floor((total_downloaded / content_length) * 100);
      defer.notify(percentage);
    });
    res.on("end", function () { defer.resolve(data); });
  });
  return defer.promise;
}

This uses the Q promises library. You would use it like this:

var promise = httpGet("http://example.com/");
promise.then(function (data) {
  // Do something with data.
}, function (reason) {
  // Do something with the error
}, function (progress) {
  // Do something with the progress update (% so far)
});