我应该在自定义函数中使用回调模式吗？ 节点js

Question

for example I have a function A that has to return some value

    function A(callback){
        //some computation
        var fakeData = 20;
        callback(null,fakeData)
    }
    function B(err,data){
      if(!err){
 console.log(data);
}

    }
A(B);

so as far as I know only I/O operations in node js runs asynchronously, so whats the difference if I right just this

   function A(){

            var fakeData = 20;
            return fakeData;
        }
        function B(data){

     console.log(data);

        }
      var data = A();
      B(data);

I mean both of them will run synchronously right?

Answer 1

The callback pattern is useful for a number of types of problems:

1. When your function uses asynchronous operations and you want to be able to notify the caller when the asynchronous operations are complete and perhaps pass a final result to the caller.

2. When your function wants the caller to supply some function that can be used in the computation of a result as in the callback that can be passed to array.sort(callback) .

You would generally NOT use a callback pattern to communicate the result of a synchronous operation because that just makes the code more complicated than just directly returning the result from the function. So, if all your operations in A() are synchronous, then your second code option will be simpler to code and use.

Answer 2

如果您在谈论这两个函数，那么是的，这两个是相同的，但这不是使用回调，因为当您有一个在一段时间后或将来会返回结果的过程（如数据库调用或REST API）时，将使用回调调用或文件读/写操作，我们不确定它们何时返回结果。