在Node.js中等待多个回调 [英] Waiting for multiple callbacks in Node.js

问题描述

我有一个Node.js应用程序，其中可能会调用多个函数，具体取决于几个因素，但在最后一次回调后只调用最后一个函数。

是我所得到的简化版本：

  if（foo === bar）{
 function1（arg1， function（val1）{
 doWhatever（val1，function（）{
 res.end（Finished）; 
}）; 
}）; 
} else if（foo === baz）{
 function2（arg2，function（val2）{
 doWhatever（val2，function（）{
 res.end ）; 
}）; 
}）; 
} else {
 function3（arg3，function（val3）{
 doWhatever（val3，function（）{
 res.end（Finished）; 
} ）; 
}）; 
} 
  

这是我在做什么：

  var finished = false; 
 
 if（foo === bar）{
 function1（arg1，function（val1）{
 result = val1; 
 finished = true; 
 }）; 
} else if（foo === baz）{
 function2（arg2，function（val2）{
 result = val2; 
 finished = true; 
}） ; 
} else {
 function3（arg3，function（val3）{
 result = val3; 
 finished = true; 
}）; 
} 
 
 var id = setInterval（function（）{
 if（finished === true）{
 clearInterval（id）; 
 doWhatever result，function（）{
 res.end（Finished）; 
}）; 
} 
}，100）; 
  

我想这可以通过使用承诺来简化，但是我不知道该怎么实现它们。你也可以使用当和承诺，哪个IMHO是最容易阅读的。

  var promises = []; 
 
 if（x）{
 var deferred1 = when.defer（）; 
 doSomethingAsync（{callback：deferred1.resolve}）; 
 promises.push（deferred1.promise）; 
} else if（y）{
 var deferred2 = when.defer（）; 
 doSomethingAsync（{callback：deferred2.resolve}）; 
 promises.push（deferred2.promise）; 
} else if（z）{
 var deferred3 = when.defer（）; 
 doSomethingAsync（{callback：deferred3.resolve}）; 
 promises.push（deferred3.promise）; 
} 
 
 when.all（promises）.then（function（）{
 console.log（'Finished Promises'）; 
}）; 
  

I have a Node.js application where multiple funcions might be called, depending on several factors, but only one last function is called after the last callback.

This is a simplified version of what I got:

if(foo === bar){
    function1(arg1, function(val1){
        doWhatever(val1, function(){
            res.end("Finished");
        });
    });
}else if(foo === baz){
    function2(arg2, function(val2){ 
        doWhatever(val2, function(){
            res.end("Finished");
        });
    });
}else{
    function3(arg3, function(val3){
        doWhatever(val3, function(){
            res.end("Finished");
        });
    });
}

And this is what im doing:

var finished = false;

if(foo === bar){
    function1(arg1, function(val1){
        result = val1;
        finished = true;
    });
}else if(foo === baz){
    function2(arg2, function(val2){ 
        result = val2;
        finished = true;
    });
}else{
    function3(arg3, function(val3){
        result = val3;
        finished = true;
    });
}

var id = setInterval(function(){
    if(finished === true){
        clearInterval(id);
        doWhatever(result, function(){
            res.end("Finished");
        });
    }
}, 100);

I guess this can be simplified by using promises, however im not sure how should I implement them.

解决方案

You could also do it using when and promises, which IMHO is the easiest to read.

var promises = [];

if(x) {
    var deferred1 = when.defer();
    doSomethingAsync({ callback: deferred1.resolve });
    promises.push(deferred1.promise);
} else if(y) {
    var deferred2 = when.defer();
    doSomethingAsync({ callback: deferred2.resolve });
    promises.push(deferred2.promise);
} else if(z) {
    var deferred3 = when.defer();
    doSomethingAsync({ callback: deferred3.resolve });
    promises.push(deferred3.promise);
}

when.all(promises).then(function () {
    console.log('Finished Promises');
});

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