javascript - 谁能告诉我这个功能是做什么的？

Question

function w_cookie_wid(wid02) {
   if ( ! document.cookie) {
      document.cookie = "w_wid=1;path=/";
      if ( ! document.cookie) {
         var w_date = new Date();
         return (w_date.getSeconds() % 20 + 1);
      }
      else return 2 - 1;
   }
   var prefix = wid02 + "=";
   var begin = document.cookie.indexOf("; " + prefix);
   if (begin == - 1) {
      begin = document.cookie.indexOf(prefix);
      if (begin != 0) {
         return null;
      }
   }
   else {
      begin += 2;
   }
   var end = document.cookie.indexOf(";", begin);
   if (end == - 1) {
      end = document.cookie.length;
   }
   return unescape(document.cookie.substring(begin + prefix.length, end));
}

Answer 1

此函数的目的是尝试从页面 cookie 中检索 cookie 值。如果未设置 cookie，该函数将尝试设置默认值 "w_wid=1;path=/" 并返回 1。如果不支持 cookie，则将返回 1 到 20 之间的半随机(基于时间)值，并且不会设置 cookie。如果设置了 cookie，该函数将尝试检索与 name 参数 (wid02) 相对应的值。如果未找到该名称，该函数将返回null，否则返回该值。

函数，用行注释:

function w_cookie_wid(wid02) {
    //if there are no cookies for this page
    if (!document.cookie) {
        //set a cookie value associated with the root
        document.cookie = "w_wid=1;path=/";
        //if there still are no cookies (not supported/allowed)
        if (!document.cookie) {
            //make a new date representing the current time
            var w_date = new Date();
            //return a number between 1 and 20
            //based on the current time
            return (w_date.getSeconds() % 20 + 1);
        }
        //return 1 if the cookie set was successful
        else return 2 - 1;
    }
    //create the name portion for a cookie value
    var prefix = wid02 + "=";
    //check to see if that value is already set,
    //but not as the first item
    var begin = document.cookie.indexOf("; " + prefix);
    //if it isn't
    if (begin == -1) {
        //check to see if it is set as the first item
        begin = document.cookie.indexOf(prefix);
        //if it isn't set (at all)
        if (begin != 0) {
            //return a null value
            return null;
        }
    }
    //if it IS set somewhere
    else {
        //set begin to be the index of beginning
        //of the name/value pair
        begin += 2;
    }
    //get the index of the first semi-colon after
    //the beginning of the name/value
    var end = document.cookie.indexOf(";", begin);
    //if there isn't one
    if (end == -1) {
        //set the end index as the length of the cookie(s)
        end = document.cookie.length;
    }
    //return the cookie name/value pair string
    return unescape(document.cookie.substring(begin + prefix.length, end));
}

请不要再要求我们做作业了。