如何在http.request函数中使用res.redirect

Question

`var req = http.request(options, function(res) 
       { 
              hh=res.headers["last-modified"]; /* hh is global variable */

       });req.end();
      /*print the last modified time of file that stored in hh
       console.log(hh);

如何在获取req.end后的hh值后使用hh？

Answer 1

请做一些关于异步代码的教程。您不了解执行顺序，我已在下面突出显示。

//this line executes at time T1.1
var req = http.request(options, function(res) {
  //This line executes at time T2.1, AFTER T1.1 and T1.2 
  hh=res.headers["last-modified"]; /* hh is global variable */
  //This line executes at time T2.2 and hh IS AVAILABLE NOW
  console.log(hh);
});
//This line executes at time T1.2
//hh is NOT SET YET. CANNOT USE IT HERE. This is what async means.
req.end();