Question

首先......新年快乐！

请您解释一下，这是如何运作的？我浏览了连接（ https://github.com/senchalabs/connect ）源代码，但我没理解。

我想自己写。

app.get(
  '/',
  function(req, res, next) {
    // Set variable        
    req.var = 'Happy new year!';
    // Go to next function
    next();
  },
  function(req, res, next) {
    // Returns 'Happy new year!' 
    console.log(req.var); // <- HOW IS THIS POSSIBLE?
    // (...)
  }      
);

提前致谢！

Answer 1

看起来你提供的第一个函数参数首先被get()函数调用。

调用时，会为呼叫提供3个参数。在调用内部，req参数必须是可以为其分配属性的对象。您已分配var属性，并为其指定了值'Happy new year!'。

通过调用next()参数调用传递的下一个函数参数，并再次向调用提供3个参数。第一个参数显然与为您分配var属性的第一个调用提供了相同的对象。

因为它（显然）是同一个对象，所以你指定的属性仍然存在。

以下是一个简单示例：http://jsfiddle.net/dWfRv/1/ （打开控制台）

// The main get() function. It has two function parameters.
function get(fn1, fn2) {
      // create an empty object that is passed as argument to both functions.
    var obj = {};
      // create a function that is passed to the first function, 
      //   which calls the second, passing it the "obj".
    var nxt = function() {
        fn2(obj); //When the first function calls this function, it fires the second.
    };
      // Call the first function, passing the "obj" and "nxt" as arguments.
    fn1(obj, nxt);
}

// Call get(), giving it two functions as parameters
get(
  function(req, next) {
      // the first function sets the req argument (which was the "obj" that was passed).
    req.msg = 'Happy new year';
      // the second function calls the next argument (which was the "nxt" function passed).
    next();
  }, 
  function(req) {
     // The second function was called by the first via "nxt",
     //   and was given the same object as the first function as the first parameter,
     //   so it still has the "msg" that you set on it.
    console.log(req.msg);
  }
);

请注意，这是一个非常简化的示例，函数中的参数较少。我还没有将var更改为msg，因为var是保留字。

Answer 2

如果需要，请尝试使用异步模块。它使得能够串联，并行或使用池更容易。

https://github.com/caolan/async

串行执行功能

2 个答案: