为什么Node.js的异步模块使用async.eachLimit第一步（数组，极限，函数，回调）后停止？

问题描述

如果我用这个code：

If I use this code:

async.eachLimit(body.photos.photo, 10, function(photo) {

         var flickr_getphoto_path = ".....";

         request.get({url: flickr_host_url + flickr_getphoto_path, json: true}, function(error, response, body) {
           if (!error && response.statusCode == 200) {

             console.log("SIZES LENGTH: " + body.sizes.size.length);
             var source_url = body.sizes.size[body.sizes.size.length - 1].source;
             request(source_url).pipe(fs.createWriteStream(path_for_downloads + path.basename(source_url)));
           }
         });

}

后10个请求（即，第一周期之后）的处理停止。
应该有10个周期。

The processing stops after 10 requests (i.e. after the first cycle).There should be 10 cycles.

是否有人知道为什么它不能正常工作？

Does somebody know why it doesn't work properly?

推荐答案

您设置了异步功能失常。第三个参数（迭代器功能）有两个参数：项目在被迭代，并且回调来告诉异步，它的完成。你错过了（因此永远不会调用）回调，因此异步不知道它的时间做下一批次。

You set up the async function wrong. The third argument (the iterator function) takes two parameters: the item being iterated upon, and a callback to tell async that it's done. You're missing (and thus never calling) the callback, so async doesn't know that it's time to do the next batch.

var async = require('async');

async.eachLimit(body.photos.photo, 10, cacheOnePhoto, function(err){
  if(err){
    console.log(err);
  } else {
    console.log('Processing complete');
  };
})

function cacheOnePhoto(photo, done){
  var flickr_getphoto_path = ".....";
  request.get({
    url: flickr_host_url + flickr_getphoto_path, 
    json: true
  }, function(error, response, body) {
    if (!error && response.statusCode == 200) {
      console.log("SIZES LENGTH: " + body.sizes.size.length);
      var source_url = body.sizes.size[body.sizes.size.length - 1].source;
      request(source_url).pipe(
        fs.createWriteStream(path_for_downloads + path.basename(source_url))
      );
      done(null);
    } else {
      done('Request error for '+flickr_getphoto_path);
    }
  });
};

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