如何在Node.js中的異步應用程序中處理模塊

Question

for (var i = 0; i < users.length; i++) {
  if (users[i].access_token !== undefined) {
    var syncer = require('dropsite_server/dbox_sync');
    var client = dboxApp.client(users[i].access_token);
    var websites_to_sync = [];
    syncer.doSync(client, users[i].website, users[i].access_token.uid);
  }
}

在syner.doSync中，我有一些異步函數調用。 是的，出於性能方面的考慮，我想讓它們保持異步。 問題在於，同步器對象只是一個引用，因此在doSync工作時，for循環將繼續運行，然后更改變量。

現在，周圍的for循環只有兩個元素，結果是僅處理了最后一個元素，但不僅處理了一次，而且實際上處理了兩次。

解決方案是使同步器成為適當的對象，但是以某種方式我失敗了。 為了更好地了解同步器中的代碼的外觀，請從以下開始：

/**
* This here is the sync module. User needs to provide. All this module does,
* is sync from a users dropbox to a local path
*/
var dbox = require("dbox");
var fs = require("fs");
var async = require("async");

var allow_downloads = true;
var allow_local_deletes = true;

var client = null;
var saved_sync_data = null;
var sync_data_path = global.config.sync_data_file;
var uid = null;
var remote_sync_dirs = null;

//var sync_data_file = ".dropbox_sync_data";

var errors = [];

var queue = async.queue(doTask, 1);

exports.doSync = function (clientIn, website_domain, _uid) {
    client = clientIn;
    uid = _uid; 
    sync_data_path = sync_data_path + "_" + uid;
    remote_sync_dirs = website_domain;
    async.series(
      [
        readSyncDataFile,
        startSync
      ]);
}
/**
 * Start the Sync
 * @param  dbox client This is a dbox client
*/

function startSync() {
  console.log("get remote delta for website: " + remote_sync_dirs)
  getRemoteDelta();
}

Answer 1

var聲明的作用域不是循環，而應在文件/函數的頂部進行

var syncer = require('dropsite_server/dbox_sync')
  , client
  , websites_to_sync = [] //what is this used for?

for (var i = 0; i < users.length; ++i) {
  if (users[i].access_token !== undefined) {
    client = dboxApp.client(users[i].access_token)
    syncer.doSync(client, users[i].website, users[i].access_token.uid);
  }
}

最后一項被處理兩次的原因是doSync函數設置模塊級別的變量，每次調用該變量都會被覆蓋。

解決此問題的方法是將變量傳遞給函數

exports.doSync = function (client, website_domain, uid) {
  sync_data_path = sync_data_path + "_" + uid
  remote_sync_dirs = website_domain

  async.series([
      readSyncDataFile.bind(null, client, website_domain, uid) 
    , startSync.bind(null, client, website_domain, uid) 
  ])
}

function startSync(client, website_domain, uid) {
  ...
}
function readSyncDataFile(client, website_domain, uid) {
  ...
}