有条件地执行回调函数

Question

如何解决以下控制流问题：

1. 只有在 someData 等于某个值或通过某些条件测试时，才想调用 getSomeOtherData

2. 在两种情况下，我都想调用 getMoreData

http.createServer(function (req, res) {
    getSomeData(client, function(someData) {
        // Only call getSomeOtherData if someData passes some conditional test
        getSomeOtherData(client, function(someOtherData) {
           // Always call getMoreData
           getMoreData(client, function(moreData) {
             res.end();
           });
       });
   });
});           

- cjroebuck

Answer 1

这个问题没有最好的解决方案；我发现最好的方法是创建一个本地函数来处理剩余的常见工作，比如：

http.createServer(function (req, res) {
  getSomeData(client, function(someData) {
    function getMoreAndEnd() {
       getMoreData(client, function(moreData) {
         res.end();
       });
    }

    if (someData) {  
      getSomeOtherData(client, function(someOtherData) {
        getMoreAndEnd();
      });
    } else {
      getMoreAndEnd();
    }
  });
}); 

- JohnnyHK

Answer 2

Is this something you want?

http.createServer(function (req, res) {
    getSomeData(client, function(someData) {
        function myFunction (callback) {
            // Only call getSomeOtherData if someData passes some conditional test
            if (someData) {
                getSomeOtherData(client, function(someOtherData) {
                   // Do something.
                });
            }

            callback();
        }

        myFunction(function () {
            // Always call getMoreData
            getMoreData(client, function(moreData) {
                res.end();
            });
        });
    });
});

- dparpyani