等待Node.js中的多个回调

我有一个Node.js应用程序,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一个最后一个函数.

这是我得到的简化版本：

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("Finished");
        });
    });
}else{
    function3(arg3,function(val3){
        doWhatever(val3,function(){
            res.end("Finished");
        });
    });
}

这就是我正在做的事情：

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promises来简化,但是我不确定应该如何实现它们.

解决方法

你也可以使用 when和promises,恕我直言,这是最容易阅读.

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');
});