NodeJS获取异步返回值（回调） [英] NodeJS get async return value (callback)

问题描述

我有这个功能，它记录到控制台，当它运行。
然而，我现在需要这个响应在另一个函数，我很努力这样做。

  var asyncJobInfo = function jobID，next）{
 
 var oozie = oozieNode.createClient（{config：config}）; 
 
 var command ='job /'+ jobID +'？show = info'; 
 
 console.log（running oozie command：+ command）; 
 
 oozie.get（命令，函数（错误，响应）{
 
 console.log（*****响应将转储到控制台：**** *）; 
 // console.log（response）; 
 return response; 
}）; 
}; 
  

这是我应该得到的：
（这显然不工作，因为它不等待响应。）

  exports.getJobInfoByID = function（req，res）{
 
 var jobIDParam = req.params.id; 
 res.send（asyncJobInfo（jobIDParam））; 
} 
  

我真的很难把我的头围绕回调，我盯着自己盲目

解决方案

回调不能返回一个值，因为他们返回的代码已经执行。

所以你可以做几件事。一个传递一个回调函数，一旦你的异步函数获取数据调用回调并传递数据。或传递响应对象并将其用于异步函数

传递回调

  exports.getJobInfoByID = function（req，res）{
 var jobIDParam = req.params.id; 
 asyncJobInfo（jobIDParam，null，function（data）{
 res.send（data）; 
}）; 
} 
 
 var asyncJobInfo = function（jobID，next，callback）{
 // ... 
 oozie.get（command，function（error，response） {
 //执行错误检查，如果ok做回调
回调（响应）; 
}）; 
}; 
 

传递响应对象

  exports.getJobInfoByID = function（req，res）{
 var jobIDParam = req.params.id; 
 asyncJobInfo（jobIDParam，null，res）; 
} 
 
 var asyncJobInfo = function（jobID，next，res）{
 // ... 
 oozie.get（command，function（error，response） {
 //执行错误检查如果确定发送响应
 res.send（response）; 
}）; 
}; 
  




I have read around the internet about callbacks but I just can't understand them in my case.

I have this function, and it logs to console when it runs. However I now need this response in another function and I am struggling to do so.

var asyncJobInfo = function(jobID, next) {

    var oozie = oozieNode.createClient({ config: config });

    var command = 'job/' + jobID + '?show=info';

    console.log("running oozie command: " + command);

    oozie.get(command, function(error, response) {

    console.log("*****response would dump to console here:*****");
//  console.log(response);
    return response;
    });
};

This is where I should get it: (This obviously doesn't work because it doesn't wait for the response.)

exports.getJobInfoByID = function(req, res) {

    var jobIDParam = req.params.id;
    res.send(asyncJobInfo(jobIDParam));
}

I really struggle to wrap my head around callbacks and I'm staring myself blind here.

解决方案

Callbacks can't return a value as the code they would be returning to has already executed.

So you can do a couple things. One pass a callback function and once your async function gets the data call the callback and pass the data. Or pass the response object and use it in your async function

Passing a callback

exports.getJobInfoByID = function(req, res) {
    var jobIDParam = req.params.id;
    asyncJobInfo(jobIDParam,null,function(data){
       res.send(data);
    });
}

var asyncJobInfo = function(jobID, next,callback) {
    //...
    oozie.get(command, function(error, response) {
       //do error check if ok do callback
       callback(response);
    });
};

Passing response object

exports.getJobInfoByID = function(req, res) {
    var jobIDParam = req.params.id;
    asyncJobInfo(jobIDParam,null,res);
}

var asyncJobInfo = function(jobID, next,res) {
    //...
    oozie.get(command, function(error, response) {
       //do error check if ok do send response
       res.send(response);
    });
};

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