串联执行功能

Question

首先...新年快乐！

您能给我解释一下，这是如何工作的？ 我浏览了整个 连接（（https://github.com/senchalabs/connect）源代码，但我不明白。

我想一个人写。

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

似乎您提供的第一个函数参数是由 get() 功能首先。

称为调用时，将提供3个参数。在呼叫中， req 参数必须是您可以分配属性的对象。您已经分配了 var 财产，并给予其价值 'Happy new year!'.

您通过的下一个函数参数是通过调用到 next() 参数和3个参数再次提供到呼叫。第一个参数显然与您分配的第一个调用给出的对象相同 var 财产。

因为（显然）是相同的对象，所以您分配的属性仍然存在。

这是一个简单的例子： http://jsfiddle.net/dwfrv/1/ （打开您的控制台）

// 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，功能中的参数较少。我也不改变 var 至 msg 自从 var 是一个保留的词。

Answer 2

如果需要，请尝试使用异步模块。能够以串联，相似或使用池的方式运行的事情变得容易得多。

https://github.com/caolan/async