Node.js：如何从回调中正确返回对象？ [英] Node.js: How to properly return an object from within a callback?

问题描述

在回调函数中定义/返回对象的正确方法是什么？

您可以在以下代码段中看到我的2个console.logs，回调之外的那个代码段当然是未定义的，我如何定义它？

在我的app.js中：

  var tools = require（'../ models / tools.js'）; 
 app.get（'/ games'，requireAuth，function（req，res）{
 var gameqlist = tools.getMyGameQs（req，function（err，gameqlist）{
 console.log gameqlist）; //这是正确定义的
 return gameqlist; //不完全正确
}）; 
 console.log（gameqlist）; //这是未定义
 res。 render（'games'，{title：'Your Games！'，gameqlist：gameqlist}）; 
 
 
}）; 
  

我有以下效用函数：

$ b b

tools.js：

  var Gameq = require（'../ models / gameq'）; 
 
 module.exports = {
 getMyGameQs：function（req，callback）{
 //查找用户所在的所有游戏队列
 Gameq 
 .find（{
'game.players.player_id'：req.user.id 
}）
 .asc（'created_at'）//按日期排序 - 获得最早的日期
 .run（function（err，gameqlist）{
 if（！gameqlist）{
 err ='你不在任何游戏中'; 
} 
 return callback ，game_list）; 
}）; 
} 
}; 
  

解决方案

你不应该这样做。回调应该是异步的，因此在调用getMyGameQs之前的代码有可能在回调之前被执行。

你应该做什么调用res.render 从内部回调。

  var tools = require（'../ models / tools.js'）; 
 app.get（'/ game'，requireAuth，function（req，res）{
 var gameqlist = tools.getMyGameQs（req，function（err，gameqlist）{
 res.render 'games'，{title：'Your Games！'，gameqlist：gameqlist}）; 
}）; 
}）; 
  

Still wrapping my head around callbacks.

What's the proper way to define/return an object from within a callback function?

You can see my 2 console.logs in the following snippet, the one outside of the callback is of course undefined, how do I define it?

In my app.js:

  var tools = require('../models/tools.js');
  app.get('/games', requireAuth, function (req, res) {
    var gameqlist = tools.getMyGameQs(req, function(err, gameqlist){
      console.log(gameqlist); // this is properly defined
      return gameqlist; // not quite right
    });
    console.log(gameqlist); // this is undefined
    res.render('games', {title:'Your Games!', gameqlist : gameqlist});


  });

I have the following utility function which works fine:

tools.js:

var Gameq = require('../models/gameq');

module.exports = {
  getMyGameQs: function (req, callback){
    // find all game queues that a user is in
    Gameq
      .find({
                'game.players.player_id' : req.user.id
                })
      .asc('created_at') // sort by date - get oldest first
      .run(function(err, gameqlist) {
        if(!gameqlist){
          err = 'You are not in any games.';
        }
        return callback(err, gameqlist); 
      });
  }
};

解决方案

You shouldn't want to do that. Callbacks are supposed to be asynchronous, so there is a chance that the code after the call to getMyGameQs is executed before the callback.

What you should do call "res.render" from inside the callback.

var tools = require('../models/tools.js');
  app.get('/games', requireAuth, function (req, res) {
    var gameqlist = tools.getMyGameQs(req, function(err, gameqlist){
      res.render('games', {title:'Your Games!', gameqlist : gameqlist});
    });
  });

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