node.js中的奇怪行为

Question

我在http://www.nodebeginner.org上读了一篇教程，我在数据输出中有一个奇怪的行为。我知道，Stackoverflow也有类似的问题，但没有答案。所以我有这个Web-Server的代码：

//server.js
var http = require('http')
var url = require('url')

function start(route, handle) {
    function onRequest(request, response) {
        var postData = ""
        var pathname = url.parse(request.url).pathname
        console.log("Request for " + pathname + " recieved.")

        request.setEncoding('utf8')
        request.addListener("data", function(postDataChunk) {
            postData += postDataChunk
            console.log("Recieved POST data chunk '" + postDataChunk +"'.")
        })

        request.addListener("end", function() {
            route(handle, pathname, response, postData)
        })
        var content = route(handle, pathname, response)
    }

    http.createServer(onRequest).listen(80, '192.168.1.34')
    console.log("Server has started")
}

exports.start = start

调用RequestHandler.Upload的Router.js代码-我的buggy函数

//router.js
function route(handle, pathname, response, postData) {
    console.log("About to route a request for " + pathname)
    if (typeof handle[pathname] === 'function') {
        handle[pathname](response, postData) //calls requestHandler.upload 
    } else {
        console.log("No request handler found for " + pathname)
        response.writeHead(404, {'Content-Type' : 'text/plain'})
        response.write("404 Not found")
        response.end()
    }
}

和RequestHandler.Upload的代码

//requestHandler.js
function upload(response, postData) {
    console.log("Request handler 'upload' was called with POST data: " + postData); //works fine
    response.writeHead(200, {"Content-Type": "text/plain"});
    response.write("You've sent: " + postData); //works ugly
    response.end();
}

假设POST数据中有一个字符串text=123。该函数的第一行输出真实数据，如“request handler'upload'was calling with POST data:text=123”。但是，这行response.write（“you ave sent：”+postData)；在浏览器中输出下一条消息:you ave sent:undefined。我做错了什么？

Answer 1

在server.js中的代码中，行：

var content = route(handle, pathname, response)

在“end”事件侦听器中的调用之前首先运行，执行函数但省略postdata参数。它运行...

response.write("You've sent: " + postData);
response.end();

因此，发送回浏览器的响应是：

You've sent: undefined

随后将触发“end”事件，事件侦听器调用...

route(handle, pathname, response, postData)

它正确地传递postdata并将其正确地输出到控制台。对response.write(...)的调用不会第二次回发到浏览器，因为此时的响应已经结束。

我希望这能解释问题所在。

var content = route(handle, pathname, response)