Javascript 循环中变量更新不正确

我一直在玩coffeescript中的node.js，从reddit.com的json接口中获取一些故事，但遇到了一些障碍

我想从

http://www.reddit.com/r/programming/.json

，然后在之后附加带有参数

count

和

的查询语句并重新分析。根据传递给
get\u stories（）

当我以
file.js>test.txt运行下面的代码时，我得到了意想不到的结果。（见下文）看起来像是
querystring.count
正在更新，但它们都与上一次传递中的URL相匹配。不知道为什么我没有看到count=0,25,50,75125。此外，
querystring.after
在URL上不存在。发生了什么事

代码：

输出：

http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125
http://www.reddit.com/r/programming/.json?count=125

[编辑]

如果需要链接异步操作，如设置
querystring.after
下一个
请求
，则在
期间将无法使用
。循环将运行到完成，在所有
请求完成之前启动所有
s，然后可以设置
querystring.after

您可以使用
函数
s将迭代重写为连续，这样每个请求都将等待，直到上一个请求中的
可用

旁注：由于
after
应该已经移动了集合的开头，因此您可能希望保持
count
相同的值。否则，集合的大小将随着每个请求而增加

get_stories = (subreddit, {per_page, pages}, storyCallback) ->
    current_page = 0

    send_next_request = (querystring = {}) ->
        querystring.count = per_page

        request_uri = "http://www.reddit.com/r/#{subreddit}/.json?#{qs.stringify querystring}"

        request
            uri: request_uri,
            json: true,
            (error, response, body) ->
                if !error and response.statusCode == 200
                    for item in body.data.children
                        if item.data.selftext_html is null
                            storyCallback request_uri, current_page, item.data

                    current_page++
                    if current_page < pages
                        send_next_request(after: body.data.children[body.data.children.length-1].id)

    send_next_request()

JavaScript和CoffeeScript（）没有块作用域，因此整个循环只创建1个
request\u uri
，并且只能保留1个值

加上
请求
是异步的，
while true
循环将在以下时间之前运行到完成：

storyCallback request_uri, current_page, item.data

对任何请求进行评估。此时，
request\u uri
将始终具有循环中给出的最后一个值

闭包创建了一个额外的
函数
作用域，因此
的每次迭代都可以有自己的
请求uri

request_uri = "http://www.reddit.com/r/#{subreddit}/.json?#{qs.stringify querystring}"

do (request_uri) ->
  request
    url: request_uri,
    # ...


这记录在：

当使用JavaScript循环生成函数时，通常会插入一个闭包包装器，以确保循环变量被关闭，并且所有生成的函数不只是共享最终值。CoffeeScript提供
do
关键字，该关键字立即调用传递的函数，转发任何参数

for filename in list
  do (filename) ->
    fs.readFile filename, (err, contents) ->
      compile filename, contents.toString()

这对uri非常有效！关于为什么
after
参数没有显示在任何URI上，您有什么见解吗？也因为代码的异步性质。有什么方法可以让它工作吗？@Kylee这是因为
while
循环已经完成，并且在任何
请求完成设置
querystring.after之前，已经启动了所有
请求。查看我的编辑了解更多信息。这很有效！我知道异步导致了很多这些问题，但不知道如何解决它们。因此，在服务器端使用Python，客户端上的JavaScript。@ Kylee，您也可以考虑使用一个“控制流”库，例如，包含异步<代码>，而 AS <代码>异步。
for filename in list
  do (filename) ->
    fs.readFile filename, (err, contents) ->
      compile filename, contents.toString()