如何检测响应滚动触发器加载的新内容?

Question

我在Facebook上运行一个脚本，要求我在我的"朋友"窗口中获得人的id(这可能不是完成此特定任务的最有效方法，但因为我想知道如何做到这一点，一般来说，这是一个很好的例子)。

这意味着，如果我有更多的朋友，我必须向下滚动Facebook将他们添加到页面。

我已经添加了将页面向下滚动到页脚的逻辑，但我不知道如何强制我的函数在内容加载后抓取id运行。

现在，我已经诉诸于使用setTimeout几秒钟-显然，这不能保证在适当的时间，所以我想知道如何正确地做到这一点:

var k;
function doit(){
    k = document.getElementsByClassName("_698");
    var g= Array.prototype.slice.call(k);
    confirm(g.length);
    // the confirm is just to make sure it's working 
    // (if i don't use setTimeout it'll return a smaller number 
    //  since not all the friends were included)
} 
window.addEventListener("load", function(){ 
  document.getElementById( "pageFooter" )
    .scrollIntoView();setTimeout(doit,3000);
  });

Answer 1

Crayon Violent在他对JavaScript检测AJAX事件的回答中详细说明了如何实现这一点。诀窍是挂钩底层XMLHttpRequest对象，以便检测何时发送请求。

我重新写了一点逻辑，使它更适合你的需要:

//
// Hooks XMLHttpRequest to log all AJAX requests. 
// Override ajaxHook.requestCompleted() to do something specific 
// in response to a given request.
//
var ajaxHook = (function()
{
   // we're using a self-executing function here to avoid polluting the global
   // namespace. The hook object is returned to expose just the properties 
   // needed by client code.
   var hook = { 
     // by default, just logs all requests to the console. 
     // Can be overridden to do something more interesting.
     requestCompleted: function(xmlHttp, url, method) { console.log(url); } 
   };
   // hook open() to store URL and method
   var oldOpen = XMLHttpRequest.prototype.open;
   XMLHttpRequest.prototype.open = function(method, url)
   {
      this.hook_method = method;
      this.hook_url = url;
      oldOpen.apply(this, arguments);
   }
   // hook send() to allow hooking onreadystatechange
   var oldSend = XMLHttpRequest.prototype.send;
   XMLHttpRequest.prototype.send = function()
   {
      var xmlhttp = this;
      //hook onreadystatechange event to allow processing results
      var oldReadyStateChange = xmlhttp.onreadystatechange;
      xmlhttp.onreadystatechange = function()
      {
         oldReadyStateChange.apply(xmlhttp, arguments);
         if ( this.readyState === 4 ) // completed
         {
            hook.requestCompleted(xmlhttp, 
              xmlhttp.hook_url, xmlhttp.hook_method);
         }
      };
      oldSend.apply(this, arguments);
   };
   return hook;
})();

在用户脚本中加载了这段代码后，您就可以实现以下逻辑:

var k;
function doit()
{
    k = document.getElementsByClassName("_698");
    var g= Array.prototype.slice.call(k);
    confirm(g.length);
} 
window.addEventListener("load", function()
{     
   ajaxHook.requestCompleted = function(xmlhttp, url, method)
   {
      // is this the request we're interested in? 
      // (Facebook appears to load friends from a URL that contains this string)
      if ( /AllFriendsAppCollectionPagelet/.test(url) ) 
      {
         // Facebook defers rendering the results here, 
         // so we just queue up scraping them until afterwards
         setTimeout(doit, 0); 
      }
   };
  // trigger loading of more friends by scrolling the bottom into view
  document.getElementById( "pageFooter" )
    .scrollIntoView();
});