首先...新年快乐!

您能给我解释一下,这是怎么工作的?我浏览了Connect的(https://github.com/senchalabs/connect)源代码,但没有得到。

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!

最佳答案

您提供的第一个函数参数似乎首先被get()函数调用。

调用时,将为该调用提供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。您已经分配了var属性,并为其赋予了'Happy new year!'值。

您传递的下一个函数参数是通过对next()参数的调用来调用的,并再次为该调用提供3个参数。第一个参数显然是与分配了var属性的第一个调用的对象相同。

因为它(显然)是同一对象,所以分配的属性仍然存在。

这是一个简单的示例: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。同样不是因为var是保留字,所以我将msg更改为var

关于javascript - 串行执行功能,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/4575691/

10-11 12:33
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